[PATCH 13/14] trailer: add interface for parsing commit trailers

From: Jeff King <peff@peff.net>
Date: Dec 29, 2015, 07:36 UTC
Message-ID: <20151229073658.GM8842@sigill.intra.peff.net>
In-Reply-To: <20151229071847.GA8726@sigill.intra.peff.net>

The git-trailer command and its subfunctions work in only one way: they take a set of trailer operations, and pass through a file while performing those operations on it.

However, other parts of the system may want to simply parse trailers, and we should be able to reuse the code here. This patch provides a simple interface for parsing a commit message with trailers, iterating over them, and retrieving individual keys.

The trailer code is a little heavy on the use of strbufs, so this is perhaps a bit slower than it would be if we were able to parse the message in place (and this speed matters when you are iterating over every commit in the repository). However, there's nothing in this interface that paints us too far into a corner; we can always optimize the internals later.

Signed-off-by: Jeff King <peff@peff.net>
---
 trailer.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 trailer.h | 31 +++++++++++++++++++++++++++++++
 2 files changed, 74 insertions(+)

diff --git a/trailer.c b/trailer.c
index 18bf209..36ba476 100644
--- a/trailer.c
+++ b/trailer.c
@@ -882,3 +882,46 @@ void process_trailers(const char *file, int trim_empty, struct string_list *trai
 
 	strbuf_list_free(lines);
 }
+
+void trailer_parse_init(struct trailer_parse_context *ctx, const struct strbuf *buf)
+{
+	int nr_lines = 0;
+
+	init_trailer_config();
+
+	ctx->lines = strbuf_split(buf, '\n');
+	while (ctx->lines[nr_lines])
+		nr_lines++;
+
+	ctx->end = find_trailer_end(ctx->lines, nr_lines);
+	ctx->start = find_trailer_start(ctx->lines, ctx->end);
+
+	strbuf_init(&ctx->token, 0);
+	strbuf_init(&ctx->value, 0);
+}
+
+void trailer_parse_clear(struct trailer_parse_context *ctx)
+{
+	strbuf_list_free(ctx->lines);
+	strbuf_release(&ctx->token);
+	strbuf_release(&ctx->value);
+}
+
+const char *trailer_parse_match(struct trailer_parse_context *ctx, int line, const char *match)
+{
+	size_t len;
+
+	if (ctx->lines[line]->buf[0] == comment_line_char)
+		return NULL;
+
+	strbuf_reset(&ctx->token);
+	strbuf_reset(&ctx->value);
+	if (parse_trailer(&ctx->token, &ctx->value, ctx->lines[line]->buf))
+		return NULL;
+
+	len = token_len_without_separator(ctx->token.buf, ctx->token.len);
+	if (strncasecmp(ctx->token.buf, match, len) || match[len])
+		return NULL;
+
+	return ctx->value.buf;
+}
diff --git a/trailer.h b/trailer.h
index 8eb25d5..1f985f6 100644
--- a/trailer.h
+++ b/trailer.h
@@ -3,4 +3,35 @@
 
 void process_trailers(const char *file, int trim_empty, struct string_list *trailers);
 
+struct trailer_parse_context {
+	struct strbuf **lines;
+	int start;
+	int end;
+
+	/* These fields are private to the parser. */
+	struct strbuf token;
+	struct strbuf value;
+};
+
+/*
+ * Parse the commit message found in "buf", looking for trailers. Any data in
+ * ctx is overwritten, and should later be freed with trailer_parse_clear().
+ *
+ * The caller can iterate over all trailers using the "start" and "end" indices
+ * into "lines".
+ */
+void trailer_parse_init(struct trailer_parse_context *ctx, const struct strbuf *buf);
+
+/*
+ * If the line contains a trailer with key "trailer", returns a pointer into
+ * "line" for the value. Otherwise, returns NULL.
+ */
+const char *trailer_parse_match(struct trailer_parse_context *ctx, int line,
+				const char *trailer);
+
+/*
+ * Free resources allocated by trailer_parse_init().
+ */
+void trailer_parse_clear(struct trailer_parse_context *ctx);
+
 #endif /* TRAILER_H */

-- 
2.7.0.rc3.367.g09631da