From 38ebffaf10d6bb23c9e6be3efcf7ec134b57b617 Mon Sep 17 00:00:00 2001
From: Aurelien DARRAGON <adarragon@haproxy.com>
Date: Thu, 5 Jan 2023 17:02:19 +0100
Subject: [PATCH] MINOR: http_htx: add http_prepend_header() to prepend value
 to header

Just like http_append_header(), but this time to insert new value before
an existing one.

If the header already contains one or multiple values, ',' is automatically
inserted after the new value.
---
 include/haproxy/http_htx.h |  1 +
 src/http_htx.c             | 57 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/include/haproxy/http_htx.h b/include/haproxy/http_htx.h
index 47f533640..3d01a061f 100644
--- a/include/haproxy/http_htx.h
+++ b/include/haproxy/http_htx.h
@@ -51,6 +51,7 @@ int http_replace_req_query(struct htx *htx, const struct ist query);
 int http_replace_res_status(struct htx *htx, const struct ist status, const struct ist reason);
 int http_replace_res_reason(struct htx *htx, const struct ist reason);
 int http_append_header_value(struct htx *htx, struct http_hdr_ctx *ctx, const struct ist data);
+int http_prepend_header_value(struct htx *htx, struct http_hdr_ctx *ctx, const struct ist data);
 int http_replace_header_value(struct htx *htx, struct http_hdr_ctx *ctx, const struct ist data);
 int http_replace_header(struct htx *htx, struct http_hdr_ctx *ctx, const struct ist name, const struct ist value);
 int http_remove_header(struct htx *htx, struct http_hdr_ctx *ctx);
diff --git a/src/http_htx.c b/src/http_htx.c
index d4fdd0705..c9d01aac8 100644
--- a/src/http_htx.c
+++ b/src/http_htx.c
@@ -591,6 +591,63 @@ int http_append_header_value(struct htx *htx, struct http_hdr_ctx *ctx, const st
 	return 0;
 }
 
+/* Prepend new value <data> before <ctx> value in header
+ * if <ctx> is not first value (at least one value exists):
+ *   - ',' delimiter is added after <data> is prepended
+ *
+ * ctx is updated to point to new value
+ *
+ * Returns 1 on success and 0 on failure.
+ */
+int http_prepend_header_value(struct htx *htx, struct http_hdr_ctx *ctx, const struct ist data)
+{
+	char *start;
+	struct htx_blk *blk = ctx->blk;
+	struct ist v;
+	uint32_t off = 0;
+	uint8_t first = 0;
+
+	if (!blk)
+		goto fail;
+
+	v = htx_get_blk_value(htx, blk);
+
+	if (!istlen(v)) {
+		start = v.ptr;
+		first = 1;
+	}
+	if (unlikely(!istlen(ctx->value)))
+		goto fail; /* invalid: value is empty, not supported */
+
+	if (!first)
+		start = istptr(ctx->value) - ctx->lws_before;
+	off = start - v.ptr;
+
+	blk = htx_replace_blk_value(htx, blk, ist2(start, 0), data);
+	if (!blk)
+		goto fail;
+	v = htx_get_blk_value(htx, blk);
+
+	if (first)
+		goto end; /* header is empty, don't append ',' */
+
+	start = v.ptr + off + data.len;
+
+	blk = htx_replace_blk_value(htx, blk, ist2(start, 0), ist(","));
+	if (!blk)
+		goto fail;
+	v = htx_get_blk_value(htx, blk);
+
+  end:
+	ctx->blk = blk;
+	ctx->value = ist2(v.ptr + off, data.len);
+	ctx->lws_before = ctx->lws_after = 0;
+
+	return 1;
+  fail:
+	return 0;
+}
+
 /* Replaces a part of a header value referenced in the context <ctx> by
  * <data>. It returns 1 on success, otherwise it returns 0. The context is
  * updated if necessary.