diff ext/serd/src/writer.c @ 226:c5cdc9e6a4bf

Add these external library files

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ext/serd/src/writer.c	Fri Jun 09 16:41:31 2017 +0100
@@ -0,0 +1,985 @@
+/*
+  Copyright 2011-2017 David Robillard <http://drobilla.net>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#include "serd_internal.h"
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define NS_RDF "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+#define NS_XSD "http://www.w3.org/2001/XMLSchema#"
+
+typedef struct {
+	SerdNode graph;
+	SerdNode subject;
+	SerdNode predicate;
+} WriteContext;
+
+static const WriteContext WRITE_CONTEXT_NULL = {
+	{ 0, 0, 0, 0, SERD_NOTHING },
+	{ 0, 0, 0, 0, SERD_NOTHING },
+	{ 0, 0, 0, 0, SERD_NOTHING }
+};
+
+typedef enum {
+	SEP_NONE,
+	SEP_END_S,       ///< End of a subject ('.')
+	SEP_END_P,       ///< End of a predicate (';')
+	SEP_END_O,       ///< End of an object (',')
+	SEP_S_P,         ///< Between a subject and predicate (whitespace)
+	SEP_P_O,         ///< Between a predicate and object (whitespace)
+	SEP_ANON_BEGIN,  ///< Start of anonymous node ('[')
+	SEP_ANON_END,    ///< End of anonymous node (']')
+	SEP_LIST_BEGIN,  ///< Start of list ('(')
+	SEP_LIST_SEP,    ///< List separator (whitespace)
+	SEP_LIST_END,    ///< End of list (')')
+	SEP_GRAPH_BEGIN, ///< Start of graph ('{')
+	SEP_GRAPH_END    ///< End of graph ('}')
+} Sep;
+
+typedef struct {
+	const char* str;               ///< Sep string
+	uint8_t     len;               ///< Length of sep string
+	uint8_t     space_before;      ///< Newline before sep
+	uint8_t     space_after_node;  ///< Newline after sep if after node
+	uint8_t     space_after_sep;   ///< Newline after sep if after sep
+} SepRule;
+
+static const SepRule rules[] = {
+	{ NULL,     0, 0, 0, 0 },
+	{ " .\n\n", 4, 0, 0, 0 },
+	{ " ;",     2, 0, 1, 1 },
+	{ " ,",     2, 0, 1, 0 },
+	{ NULL,     0, 0, 1, 0 },
+	{ " ",      1, 0, 0, 0 },
+	{ "[",      1, 0, 1, 1 },
+	{ "]",      1, 1, 0, 0 },
+	{ "(",      1, 0, 0, 0 },
+	{ NULL,     1, 0, 1, 0 },
+	{ ")",      1, 1, 0, 0 },
+	{ " {",     2, 0, 1, 1 },
+	{ " }",     2, 0, 1, 1 },
+	{ "\n",     1, 0, 1, 0 }
+};
+
+struct SerdWriterImpl {
+	SerdSyntax    syntax;
+	SerdStyle     style;
+	SerdEnv*      env;
+	SerdNode      root_node;
+	SerdURI       root_uri;
+	SerdURI       base_uri;
+	SerdStack     anon_stack;
+	SerdByteSink  byte_sink;
+	SerdErrorSink error_sink;
+	void*         error_handle;
+	WriteContext  context;
+	SerdNode      list_subj;
+	unsigned      list_depth;
+	unsigned      indent;
+	uint8_t*      bprefix;
+	size_t        bprefix_len;
+	Sep           last_sep;
+	bool          empty;
+};
+
+typedef enum {
+	WRITE_STRING,
+	WRITE_LONG_STRING
+} TextContext;
+
+static bool
+supports_abbrev(const SerdWriter* writer)
+{
+	return writer->syntax == SERD_TURTLE || writer->syntax == SERD_TRIG;
+}
+
+static void
+w_err(SerdWriter* writer, SerdStatus st, const char* fmt, ...)
+{
+	/* TODO: This results in errors with no file information, which is not
+	   helpful when re-serializing a file (particularly for "undefined
+	   namespace prefix" errors.  The statement sink API needs to be changed to
+	   add a Cursor parameter so the source can notify the writer of the
+	   statement origin for better error reporting. */
+
+	va_list args;
+	va_start(args, fmt);
+	const SerdError e = { st, NULL, 0, 0, fmt, &args };
+	serd_error(writer->error_sink, writer->error_handle, &e);
+	va_end(args);
+}
+
+static inline WriteContext*
+anon_stack_top(SerdWriter* writer)
+{
+	assert(!serd_stack_is_empty(&writer->anon_stack));
+	return (WriteContext*)(writer->anon_stack.buf
+	                       + writer->anon_stack.size - sizeof(WriteContext));
+}
+
+static void
+copy_node(SerdNode* dst, const SerdNode* src)
+{
+	if (src) {
+		dst->buf = (uint8_t*)realloc((char*)dst->buf, src->n_bytes + 1);
+		dst->n_bytes = src->n_bytes;
+		dst->n_chars = src->n_chars;
+		dst->flags   = src->flags;
+		dst->type    = src->type;
+		memcpy((char*)dst->buf, src->buf, src->n_bytes + 1);
+	} else {
+		dst->type = SERD_NOTHING;
+	}
+}
+
+static inline size_t
+sink(const void* buf, size_t len, SerdWriter* writer)
+{
+	return serd_byte_sink_write(buf, len, &writer->byte_sink);
+}
+
+// Parse a UTF-8 character, set *size to the length, and return the code point
+static inline uint32_t
+parse_utf8_char(SerdWriter* writer, const uint8_t* utf8, size_t* size)
+{
+	uint32_t c = 0;
+	if ((utf8[0] & 0x80) == 0) {  // Starts with `0'
+		*size = 1;
+		c     = utf8[0];
+	} else if ((utf8[0] & 0xE0) == 0xC0) {  // Starts with `110'
+		*size = 2;
+		c     = utf8[0] & 0x1F;
+	} else if ((utf8[0] & 0xF0) == 0xE0) {  // Starts with `1110'
+		*size = 3;
+		c     = utf8[0] & 0x0F;
+	} else if ((utf8[0] & 0xF8) == 0xF0) {  // Starts with `11110'
+		*size = 4;
+		c     = utf8[0] & 0x07;
+	} else {
+		w_err(writer, SERD_ERR_BAD_ARG, "invalid UTF-8: %X\n", utf8[0]);
+		*size = 0;
+		return 0;
+	}
+
+	size_t  i  = 0;
+	uint8_t in = utf8[i++];
+
+#define READ_BYTE() \
+	in = utf8[i++] & 0x3F; \
+	c  = (c << 6) | in;
+
+	switch (*size) {
+	case 4: READ_BYTE();
+	case 3: READ_BYTE();
+	case 2: READ_BYTE();
+	}
+
+	return c;
+}
+
+// Write a single character, as an escape for single byte characters
+// (Caller prints any single byte characters that don't need escaping)
+static size_t
+write_character(SerdWriter* writer, const uint8_t* utf8, size_t* size)
+{
+	const uint8_t replacement_char[] = { 0xEF, 0xBF, 0xBD };
+	char          escape[11]         = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
+	const uint8_t in                 = utf8[0];
+
+	uint32_t c = parse_utf8_char(writer, utf8, size);
+	switch (*size) {
+	case 0:
+		w_err(writer, SERD_ERR_BAD_ARG, "invalid UTF-8: %X\n", in);
+		return sink(replacement_char, sizeof(replacement_char), writer);
+	case 1:
+		snprintf(escape, sizeof(escape), "\\u%04X", in);
+		return sink(escape, 6, writer);
+	default:
+		break;
+	}
+
+	if (!(writer->style & SERD_STYLE_ASCII)) {
+		// Write UTF-8 character directly to UTF-8 output
+		return sink(utf8, *size, writer);
+	}
+
+	if (c <= 0xFFFF) {
+		snprintf(escape, sizeof(escape), "\\u%04X", c);
+		return sink(escape, 6, writer);
+	} else {
+		snprintf(escape, sizeof(escape), "\\U%08X", c);
+		return sink(escape, 10, writer);
+	}
+}
+
+static inline bool
+uri_must_escape(const uint8_t c)
+{
+	switch (c) {
+	case ' ': case '"': case '<': case '>': case '\\':
+	case '^': case '`': case '{': case '|': case '}':
+		return true;
+	default:
+		return !in_range(c, 0x20, 0x7E);
+	}
+}
+
+static size_t
+write_uri(SerdWriter* writer, const uint8_t* utf8, size_t n_bytes)
+{
+	size_t len = 0;
+	for (size_t i = 0; i < n_bytes;) {
+		size_t j = i;  // Index of next character that must be escaped
+		for (; j < n_bytes; ++j) {
+			if (uri_must_escape(utf8[j])) {
+				break;
+			}
+		}
+
+		// Bulk write all characters up to this special one
+		len += sink(&utf8[i], j - i, writer);
+		if ((i = j) == n_bytes) {
+			break;  // Reached end
+		}
+
+		// Write UTF-8 character
+		size_t size = 0;
+		len += write_character(writer, utf8 + i, &size);
+		i   += size;
+	}
+	return len;
+}
+
+static bool
+lname_must_escape(const uint8_t c)
+{
+	/* This arbitrary list of characters, most of which have nothing to do with
+	   Turtle, must be handled as special cases here because the RDF and SPARQL
+	   WGs are apparently intent on making the once elegant Turtle a baroque
+	   and inconsistent mess, throwing elegance and extensibility completely
+	   out the window for no good reason.
+
+	   Note '-', '.', and '_' are also in PN_LOCAL_ESC, but are valid unescaped
+	   in local names, so they are not escaped here. */
+
+	switch (c) {
+	case '\'': case '!': case '#': case '$': case '%': case '&':
+	case '(': case ')': case '*': case '+': case ',': case '/':
+	case ';': case '=': case '?': case '@': case '~':
+		return true;
+	}
+	return false;
+}
+
+static size_t
+write_lname(SerdWriter* writer, const uint8_t* utf8, size_t n_bytes)
+{
+	size_t len = 0;
+	for (size_t i = 0; i < n_bytes; ++i) {
+		size_t j = i;  // Index of next character that must be escaped
+		for (; j < n_bytes; ++j) {
+			if (lname_must_escape(utf8[j])) {
+				break;
+			}
+		}
+
+		// Bulk write all characters up to this special one
+		len += sink(&utf8[i], j - i, writer);
+		if ((i = j) == n_bytes) {
+			break;  // Reached end
+		}
+
+		// Write escape
+		len += sink("\\", 1, writer);
+		len += sink(&utf8[i], 1, writer);
+	}
+	return len;
+}
+
+static size_t
+write_text(SerdWriter* writer, TextContext ctx,
+           const uint8_t* utf8, size_t n_bytes)
+{
+	size_t len = 0;
+	for (size_t i = 0; i < n_bytes;) {
+		// Fast bulk write for long strings of printable ASCII
+		size_t j = i;
+		for (; j < n_bytes; ++j) {
+			if (utf8[j] == '\\' || utf8[j] == '"'
+			    || (!in_range(utf8[j], 0x20, 0x7E))) {
+				break;
+			}
+		}
+
+		len += sink(&utf8[i], j - i, writer);
+		if ((i = j) == n_bytes) {
+			break;  // Reached end
+		}
+
+		uint8_t in = utf8[i++];
+		if (ctx == WRITE_LONG_STRING) {
+			switch (in) {
+			case '\\': len += sink("\\\\", 2, writer); continue;
+			case '\b': len += sink("\\b", 2, writer);  continue;
+			case '\n': case '\r': case '\t': case '\f':
+				len += sink(&in, 1, writer);  // Write character as-is
+				continue;
+			case '\"':
+				if (i == n_bytes) {  // '"' at string end
+					len += sink("\\\"", 2, writer);
+				} else {
+					len += sink(&in, 1, writer);
+				}
+				continue;
+			default: break;
+			}
+		} else if (ctx == WRITE_STRING) {
+			switch (in) {
+			case '\\': len += sink("\\\\", 2, writer); continue;
+			case '\n': len += sink("\\n", 2, writer);  continue;
+			case '\r': len += sink("\\r", 2, writer);  continue;
+			case '\t': len += sink("\\t", 2, writer);  continue;
+			case '"':  len += sink("\\\"", 2, writer); continue;
+			default: break;
+			}
+			if (writer->syntax == SERD_TURTLE) {
+				switch (in) {
+				case '\b': len += sink("\\b", 2, writer); continue;
+				case '\f': len += sink("\\f", 2, writer); continue;
+				}
+			}
+		}
+
+		size_t size = 0;
+		len += write_character(writer, utf8 + i - 1, &size);
+
+		if (size == 0) {
+			return len;
+		}
+
+		i += size - 1;
+	}
+	return len;
+}
+
+static size_t
+uri_sink(const void* buf, size_t len, void* stream)
+{
+	return write_uri((SerdWriter*)stream, (const uint8_t*)buf, len);
+}
+
+static void
+write_newline(SerdWriter* writer)
+{
+	sink("\n", 1, writer);
+	for (unsigned i = 0; i < writer->indent; ++i) {
+		sink("\t", 1, writer);
+	}
+}
+
+static void
+write_sep(SerdWriter* writer, const Sep sep)
+{
+	const SepRule* rule = &rules[sep];
+	if (rule->space_before) {
+		write_newline(writer);
+	}
+	if (rule->str) {
+		sink(rule->str, rule->len, writer);
+	}
+	if (    (writer->last_sep && rule->space_after_sep)
+	    || (!writer->last_sep && rule->space_after_node)) {
+		write_newline(writer);
+	} else if (writer->last_sep && rule->space_after_node) {
+		sink(" ", 1, writer);
+	}
+	writer->last_sep = sep;
+}
+
+static SerdStatus
+reset_context(SerdWriter* writer, bool graph)
+{
+	if (graph) {
+		writer->context.graph.type = SERD_NOTHING;
+	}
+	writer->context.subject.type   = SERD_NOTHING;
+	writer->context.predicate.type = SERD_NOTHING;
+	writer->empty                  = false;
+	return SERD_SUCCESS;
+}
+
+static SerdStatus
+free_context(SerdWriter* writer)
+{
+	serd_node_free(&writer->context.graph);
+	serd_node_free(&writer->context.subject);
+	serd_node_free(&writer->context.predicate);
+	return reset_context(writer, true);
+}
+
+typedef enum {
+	FIELD_NONE,
+	FIELD_SUBJECT,
+	FIELD_PREDICATE,
+	FIELD_OBJECT,
+	FIELD_GRAPH
+} Field;
+
+static bool
+is_inline_start(const SerdWriter* writer, Field field, SerdStatementFlags flags)
+{
+	return (supports_abbrev(writer) &&
+	        ((field == FIELD_SUBJECT && (flags & SERD_ANON_S_BEGIN)) ||
+	         (field == FIELD_OBJECT &&  (flags & SERD_ANON_O_BEGIN))));
+}
+
+static bool
+write_node(SerdWriter*        writer,
+           const SerdNode*    node,
+           const SerdNode*    datatype,
+           const SerdNode*    lang,
+           Field              field,
+           SerdStatementFlags flags)
+{
+	SerdChunk uri_prefix;
+	SerdNode  prefix;
+	SerdChunk suffix;
+	bool      has_scheme;
+	switch (node->type) {
+	case SERD_BLANK:
+		if (is_inline_start(writer, field, flags)) {
+			++writer->indent;
+			write_sep(writer, SEP_ANON_BEGIN);
+		} else if (supports_abbrev(writer)
+		           && (field == FIELD_SUBJECT && (flags & SERD_LIST_S_BEGIN))) {
+			assert(writer->list_depth == 0);
+			copy_node(&writer->list_subj, node);
+			++writer->list_depth;
+			++writer->indent;
+			write_sep(writer, SEP_LIST_BEGIN);
+		} else if (supports_abbrev(writer)
+		           && (field == FIELD_OBJECT && (flags & SERD_LIST_O_BEGIN))) {
+			++writer->indent;
+			++writer->list_depth;
+			write_sep(writer, SEP_LIST_BEGIN);
+		} else if (supports_abbrev(writer)
+		           && ((field == FIELD_SUBJECT && (flags & SERD_EMPTY_S))
+		               || (field == FIELD_OBJECT && (flags & SERD_EMPTY_O)))) {
+			sink("[]", 2, writer);
+		} else {
+			sink("_:", 2, writer);
+			if (writer->bprefix && !strncmp((const char*)node->buf,
+			                                (const char*)writer->bprefix,
+			                                writer->bprefix_len)) {
+				sink(node->buf + writer->bprefix_len,
+				     node->n_bytes - writer->bprefix_len,
+				     writer);
+			} else {
+				sink(node->buf, node->n_bytes, writer);
+			}
+		}
+		break;
+	case SERD_CURIE:
+		switch (writer->syntax) {
+		case SERD_NTRIPLES:
+		case SERD_NQUADS:
+			if (serd_env_expand(writer->env, node, &uri_prefix, &suffix)) {
+				w_err(writer, SERD_ERR_BAD_CURIE,
+				      "undefined namespace prefix `%s'\n", node->buf);
+				return false;
+			}
+			sink("<", 1, writer);
+			write_uri(writer, uri_prefix.buf, uri_prefix.len);
+			write_uri(writer, suffix.buf, suffix.len);
+			sink(">", 1, writer);
+			break;
+		case SERD_TURTLE:
+		case SERD_TRIG:
+			if (is_inline_start(writer, field, flags)) {
+				++writer->indent;
+				write_sep(writer, SEP_ANON_BEGIN);
+				sink("== ", 3, writer);
+			}
+			write_lname(writer, node->buf, node->n_bytes);
+			if (is_inline_start(writer, field, flags)) {
+				sink(" ;", 2, writer);
+				write_newline(writer);
+			}
+		}
+		break;
+	case SERD_LITERAL:
+		if (supports_abbrev(writer) && datatype && datatype->buf) {
+			const char* type_uri = (const char*)datatype->buf;
+			if (!strncmp(type_uri, NS_XSD, sizeof(NS_XSD) - 1) && (
+				    !strcmp(type_uri + sizeof(NS_XSD) - 1, "boolean") ||
+				    !strcmp(type_uri + sizeof(NS_XSD) - 1, "integer"))) {
+				sink(node->buf, node->n_bytes, writer);
+				break;
+			} else if (!strncmp(type_uri, NS_XSD, sizeof(NS_XSD) - 1) &&
+			           !strcmp(type_uri + sizeof(NS_XSD) - 1, "decimal") &&
+			           strchr((const char*)node->buf, '.') &&
+			           node->buf[node->n_bytes - 1] != '.') {
+				/* xsd:decimal literals without trailing digits, e.g. "5.", can
+				   not be written bare in Turtle.  We could add a 0 which is
+				   prettier, but changes the text and breaks round tripping.
+				*/
+				sink(node->buf, node->n_bytes, writer);
+				break;
+			}
+		}
+		if (supports_abbrev(writer)
+		    && (node->flags & (SERD_HAS_NEWLINE|SERD_HAS_QUOTE))) {
+			sink("\"\"\"", 3, writer);
+			write_text(writer, WRITE_LONG_STRING, node->buf, node->n_bytes);
+			sink("\"\"\"", 3, writer);
+		} else {
+			sink("\"", 1, writer);
+			write_text(writer, WRITE_STRING, node->buf, node->n_bytes);
+			sink("\"", 1, writer);
+		}
+		if (lang && lang->buf) {
+			sink("@", 1, writer);
+			sink(lang->buf, lang->n_bytes, writer);
+		} else if (datatype && datatype->buf) {
+			sink("^^", 2, writer);
+			write_node(writer, datatype, NULL, NULL, FIELD_NONE, flags);
+		}
+		break;
+	case SERD_URI:
+		if (is_inline_start(writer, field, flags)) {
+			++writer->indent;
+			write_sep(writer, SEP_ANON_BEGIN);
+			sink("== ", 3, writer);
+		}
+		has_scheme = serd_uri_string_has_scheme(node->buf);
+		if (field == FIELD_PREDICATE && supports_abbrev(writer)
+		    && !strcmp((const char*)node->buf, NS_RDF "type")) {
+			sink("a", 1, writer);
+			break;
+		} else if (supports_abbrev(writer)
+		           && !strcmp((const char*)node->buf, NS_RDF "nil")) {
+			sink("()", 2, writer);
+			break;
+		} else if (has_scheme && (writer->style & SERD_STYLE_CURIED) &&
+		           serd_env_qualify(writer->env, node, &prefix, &suffix)) {
+			write_uri(writer, prefix.buf, prefix.n_bytes);
+			sink(":", 1, writer);
+			write_uri(writer, suffix.buf, suffix.len);
+			break;
+		}
+		sink("<", 1, writer);
+		if (writer->style & SERD_STYLE_RESOLVED) {
+			SerdURI in_base_uri, uri, abs_uri;
+			serd_env_get_base_uri(writer->env, &in_base_uri);
+			serd_uri_parse(node->buf, &uri);
+			serd_uri_resolve(&uri, &in_base_uri, &abs_uri);
+			bool rooted = uri_is_under(&writer->base_uri, &writer->root_uri);
+			SerdURI* root = rooted ? &writer->root_uri : & writer->base_uri;
+			if (!uri_is_under(&abs_uri, root) ||
+			    writer->syntax == SERD_NTRIPLES ||
+			    writer->syntax == SERD_NQUADS) {
+				serd_uri_serialise(&abs_uri, uri_sink, writer);
+			} else {
+				serd_uri_serialise_relative(
+					&uri, &writer->base_uri, root, uri_sink, writer);
+			}
+		} else {
+			write_uri(writer, node->buf, node->n_bytes);
+		}
+		sink(">", 1, writer);
+		if (is_inline_start(writer, field, flags)) {
+			sink(" ;", 2, writer);
+			write_newline(writer);
+		}
+	default:
+		break;
+	}
+	writer->last_sep = SEP_NONE;
+	return true;
+}
+
+static inline bool
+is_resource(const SerdNode* node)
+{
+	return node->type > SERD_LITERAL;
+}
+
+static void
+write_pred(SerdWriter* writer, SerdStatementFlags flags, const SerdNode* pred)
+{
+	write_node(writer, pred, NULL, NULL, FIELD_PREDICATE, flags);
+	write_sep(writer, SEP_P_O);
+	copy_node(&writer->context.predicate, pred);
+}
+
+static bool
+write_list_obj(SerdWriter*        writer,
+               SerdStatementFlags flags,
+               const SerdNode*    predicate,
+               const SerdNode*    object,
+               const SerdNode*    datatype,
+               const SerdNode*    lang)
+{
+	if (!strcmp((const char*)object->buf, NS_RDF "nil")) {
+		--writer->indent;
+		write_sep(writer, SEP_LIST_END);
+		return true;
+	} else if (!strcmp((const char*)predicate->buf, NS_RDF "first")) {
+		write_sep(writer, SEP_LIST_SEP);
+		write_node(writer, object, datatype, lang, FIELD_OBJECT, flags);
+	}
+	return false;
+}
+
+SERD_API
+SerdStatus
+serd_writer_write_statement(SerdWriter*        writer,
+                            SerdStatementFlags flags,
+                            const SerdNode*    graph,
+                            const SerdNode*    subject,
+                            const SerdNode*    predicate,
+                            const SerdNode*    object,
+                            const SerdNode*    datatype,
+                            const SerdNode*    lang)
+{
+	if (!subject || !predicate || !object
+	    || !subject->buf || !predicate->buf || !object->buf
+	    || !is_resource(subject) || !is_resource(predicate)) {
+		return SERD_ERR_BAD_ARG;
+	}
+
+#define TRY(write_result) \
+	if (!write_result) { \
+		return SERD_ERR_UNKNOWN; \
+	}
+
+	switch (writer->syntax) {
+	case SERD_NTRIPLES:
+	case SERD_NQUADS:
+		TRY(write_node(writer, subject, NULL, NULL, FIELD_SUBJECT, flags));
+		sink(" ", 1, writer);
+		TRY(write_node(writer, predicate, NULL, NULL, FIELD_PREDICATE, flags));
+		sink(" ", 1, writer);
+		TRY(write_node(writer, object, datatype, lang, FIELD_OBJECT, flags));
+		if (writer->syntax == SERD_NQUADS && graph) {
+			sink(" ", 1, writer);
+			TRY(write_node(writer, graph, datatype, lang, FIELD_GRAPH, flags));
+		}
+		sink(" .\n", 3, writer);
+		return SERD_SUCCESS;
+	default:
+		break;
+	}
+
+	if ((graph && !serd_node_equals(graph, &writer->context.graph)) ||
+	    (!graph && writer->context.graph.type)) {
+		writer->indent = 0;
+		if (writer->context.subject.type) {
+			write_sep(writer, SEP_END_S);
+		}
+		if (writer->context.graph.type) {
+			write_sep(writer, SEP_GRAPH_END);
+		}
+
+		reset_context(writer, true);
+		if (graph) {
+			TRY(write_node(writer, graph, datatype, lang, FIELD_GRAPH, flags));
+			++writer->indent;
+			write_sep(writer, SEP_GRAPH_BEGIN);
+			copy_node(&writer->context.graph, graph);
+		}
+	}
+
+	if ((flags & SERD_LIST_CONT)) {
+		if (write_list_obj(writer, flags, predicate, object, datatype, lang)) {
+			// Reached end of list
+			if (--writer->list_depth == 0 && writer->list_subj.type) {
+				reset_context(writer, false);
+				serd_node_free(&writer->context.subject);
+				writer->context.subject = writer->list_subj;
+				writer->list_subj       = SERD_NODE_NULL;
+			}
+			return SERD_SUCCESS;
+		}
+	} else if (serd_node_equals(subject, &writer->context.subject)) {
+		if (serd_node_equals(predicate, &writer->context.predicate)) {
+			// Abbreviate S P
+			if (!(flags & SERD_ANON_O_BEGIN)) {
+				++writer->indent;
+			}
+			write_sep(writer, SEP_END_O);
+			write_node(writer, object, datatype, lang, FIELD_OBJECT, flags);
+			if (!(flags & SERD_ANON_O_BEGIN)) {
+				--writer->indent;
+			}
+		} else {
+			// Abbreviate S
+			Sep sep = writer->context.predicate.type ? SEP_END_P : SEP_S_P;
+			write_sep(writer, sep);
+			write_pred(writer, flags, predicate);
+			write_node(writer, object, datatype, lang, FIELD_OBJECT, flags);
+		}
+	} else {
+		// No abbreviation
+		if (writer->context.subject.type) {
+			assert(writer->indent > 0);
+			--writer->indent;
+			if (serd_stack_is_empty(&writer->anon_stack)) {
+				write_sep(writer, SEP_END_S);
+			}
+		} else if (!writer->empty) {
+			write_sep(writer, SEP_S_P);
+		}
+
+		if (!(flags & SERD_ANON_CONT)) {
+			write_node(writer, subject, NULL, NULL, FIELD_SUBJECT, flags);
+			++writer->indent;
+			write_sep(writer, SEP_S_P);
+		} else {
+			++writer->indent;
+		}
+
+		reset_context(writer, false);
+		copy_node(&writer->context.subject, subject);
+
+		if (!(flags & SERD_LIST_S_BEGIN)) {
+			write_pred(writer, flags, predicate);
+		}
+
+		write_node(writer, object, datatype, lang, FIELD_OBJECT, flags);
+	}
+
+	if (flags & (SERD_ANON_S_BEGIN|SERD_ANON_O_BEGIN)) {
+		WriteContext* ctx = (WriteContext*)serd_stack_push(
+			&writer->anon_stack, sizeof(WriteContext));
+		*ctx = writer->context;
+		WriteContext new_context = {
+			serd_node_copy(graph), serd_node_copy(subject), SERD_NODE_NULL };
+		if ((flags & SERD_ANON_S_BEGIN)) {
+			new_context.predicate = serd_node_copy(predicate);
+		}
+		writer->context = new_context;
+	} else {
+		copy_node(&writer->context.graph, graph);
+		copy_node(&writer->context.subject, subject);
+		copy_node(&writer->context.predicate, predicate);
+	}
+
+	return SERD_SUCCESS;
+}
+
+SERD_API
+SerdStatus
+serd_writer_end_anon(SerdWriter*     writer,
+                     const SerdNode* node)
+{
+	if (writer->syntax == SERD_NTRIPLES || writer->syntax == SERD_NQUADS) {
+		return SERD_SUCCESS;
+	}
+	if (serd_stack_is_empty(&writer->anon_stack) || writer->indent == 0) {
+		w_err(writer, SERD_ERR_UNKNOWN,
+		      "unexpected end of anonymous node\n");
+		return SERD_ERR_UNKNOWN;
+	}
+	--writer->indent;
+	write_sep(writer, SEP_ANON_END);
+	free_context(writer);
+	writer->context = *anon_stack_top(writer);
+	serd_stack_pop(&writer->anon_stack, sizeof(WriteContext));
+	const bool is_subject = serd_node_equals(node, &writer->context.subject);
+	if (is_subject) {
+		copy_node(&writer->context.subject, node);
+		writer->context.predicate.type = SERD_NOTHING;
+	}
+	return SERD_SUCCESS;
+}
+
+SERD_API
+SerdStatus
+serd_writer_finish(SerdWriter* writer)
+{
+	if (writer->context.subject.type) {
+		sink(" .\n", 3, writer);
+	}
+	if (writer->context.graph.type) {
+		sink("}\n", 2, writer);
+	}
+	serd_byte_sink_flush(&writer->byte_sink);
+	writer->indent = 0;
+	return free_context(writer);
+}
+
+SERD_API
+SerdWriter*
+serd_writer_new(SerdSyntax     syntax,
+                SerdStyle      style,
+                SerdEnv*       env,
+                const SerdURI* base_uri,
+                SerdSink       ssink,
+                void*          stream)
+{
+	const WriteContext context = WRITE_CONTEXT_NULL;
+	SerdWriter*        writer  = (SerdWriter*)calloc(1, sizeof(SerdWriter));
+	writer->syntax       = syntax;
+	writer->style        = style;
+	writer->env          = env;
+	writer->root_node    = SERD_NODE_NULL;
+	writer->root_uri     = SERD_URI_NULL;
+	writer->base_uri     = base_uri ? *base_uri : SERD_URI_NULL;
+	writer->anon_stack   = serd_stack_new(sizeof(WriteContext));
+	writer->context      = context;
+	writer->list_subj    = SERD_NODE_NULL;
+	writer->empty        = true;
+	writer->byte_sink    = serd_byte_sink_new(
+		ssink, stream, (style & SERD_STYLE_BULK) ? SERD_PAGE_SIZE : 1);
+	return writer;
+}
+
+SERD_API
+void
+serd_writer_set_error_sink(SerdWriter*   writer,
+                           SerdErrorSink error_sink,
+                           void*         error_handle)
+{
+	writer->error_sink   = error_sink;
+	writer->error_handle = error_handle;
+}
+
+SERD_API
+void
+serd_writer_chop_blank_prefix(SerdWriter*    writer,
+                              const uint8_t* prefix)
+{
+	free(writer->bprefix);
+	writer->bprefix_len = 0;
+	writer->bprefix     = NULL;
+	if (prefix) {
+		writer->bprefix_len = strlen((const char*)prefix);
+		writer->bprefix     = (uint8_t*)malloc(writer->bprefix_len + 1);
+		memcpy(writer->bprefix, prefix, writer->bprefix_len + 1);
+	}
+}
+
+SERD_API
+SerdStatus
+serd_writer_set_base_uri(SerdWriter*     writer,
+                         const SerdNode* uri)
+{
+	if (!serd_env_set_base_uri(writer->env, uri)) {
+		serd_env_get_base_uri(writer->env, &writer->base_uri);
+
+		if (writer->syntax == SERD_TURTLE || writer->syntax == SERD_TRIG) {
+			if (writer->context.graph.type || writer->context.subject.type) {
+				sink(" .\n\n", 4, writer);
+				reset_context(writer, true);
+			}
+			sink("@base <", 7, writer);
+			sink(uri->buf, uri->n_bytes, writer);
+			sink("> .\n", 4, writer);
+		}
+		writer->indent = 0;
+		return reset_context(writer, true);
+	}
+	return SERD_ERR_UNKNOWN;
+}
+
+SERD_API
+SerdStatus
+serd_writer_set_root_uri(SerdWriter*     writer,
+                         const SerdNode* uri)
+{
+	serd_node_free(&writer->root_node);
+	if (uri && uri->buf) {
+		writer->root_node = serd_node_copy(uri);
+		serd_uri_parse(uri->buf, &writer->root_uri);
+	} else {
+		writer->root_node = SERD_NODE_NULL;
+		writer->root_uri  = SERD_URI_NULL;
+	}
+	return SERD_SUCCESS;
+}
+
+SERD_API
+SerdStatus
+serd_writer_set_prefix(SerdWriter*     writer,
+                       const SerdNode* name,
+                       const SerdNode* uri)
+{
+	if (!serd_env_set_prefix(writer->env, name, uri)) {
+		if (writer->syntax == SERD_TURTLE || writer->syntax == SERD_TRIG) {
+			if (writer->context.graph.type || writer->context.subject.type) {
+				sink(" .\n\n", 4, writer);
+				reset_context(writer, true);
+			}
+			sink("@prefix ", 8, writer);
+			sink(name->buf, name->n_bytes, writer);
+			sink(": <", 3, writer);
+			write_uri(writer, uri->buf, uri->n_bytes);
+			sink("> .\n", 4, writer);
+		}
+		writer->indent = 0;
+		return reset_context(writer, true);
+	}
+	return SERD_ERR_UNKNOWN;
+}
+
+SERD_API
+void
+serd_writer_free(SerdWriter* writer)
+{
+	serd_writer_finish(writer);
+	serd_stack_free(&writer->anon_stack);
+	free(writer->bprefix);
+	serd_byte_sink_free(&writer->byte_sink);
+	serd_node_free(&writer->root_node);
+	free(writer);
+}
+
+SERD_API
+SerdEnv*
+serd_writer_get_env(SerdWriter* writer)
+{
+	return writer->env;
+}
+
+SERD_API
+size_t
+serd_file_sink(const void* buf, size_t len, void* stream)
+{
+	return fwrite(buf, 1, len, (FILE*)stream);
+}
+
+SERD_API
+size_t
+serd_chunk_sink(const void* buf, size_t len, void* stream)
+{
+	SerdChunk* chunk = (SerdChunk*)stream;
+	chunk->buf = (uint8_t*)realloc((uint8_t*)chunk->buf, chunk->len + len);
+	memcpy((uint8_t*)chunk->buf + chunk->len, buf, len);
+	chunk->len += len;
+	return len;
+}
+
+SERD_API
+uint8_t*
+serd_chunk_sink_finish(SerdChunk* stream)
+{
+	serd_chunk_sink("", 1, stream);
+	return (uint8_t*)stream->buf;
+}