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Merged
DeusData merged 1 commit into from
Jun 23, 2026
+143 −1
Merged

fix(mcp): return valid UTF-8 snippets #526

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77 changes: 76 additions & 1 deletion src/mcp/mcp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2833,6 +2833,75 @@ static char *resolve_snippet_source(const char *root_path, const char *file_path
return NULL;
}

static bool utf8_is_cont(unsigned char c) {
return (c & 0xC0) == 0x80;
}

static char *sanitize_utf8_lossy(const char *s) {
enum {
UTF8_REPLACEMENT_LEN = 3,
UTF8_THREE_BYTE_LEN = 3,
UTF8_FOUR_BYTE_LEN = 4,
UTF8_FOURTH_BYTE = 3,
};
if (!s) {
return NULL;
}
size_t len = strlen(s);
if (len > (((size_t)-1) - SKIP_ONE) / UTF8_REPLACEMENT_LEN) {
return NULL;
}
char *out = malloc(len * UTF8_REPLACEMENT_LEN + SKIP_ONE);
if (!out) {
return NULL;
}

const unsigned char *p = (const unsigned char *)s;
const unsigned char *end = p + len;
unsigned char *dst = (unsigned char *)out;
while (p < end) {
unsigned char c = *p;
size_t n = 0;
if (c < 0x80) {
n = 1;
} else if (c >= 0xC2 && c <= 0xDF && p + 1 < end && utf8_is_cont(p[1])) {
n = 2;
} else if (c == 0xE0 && p + 2 < end && p[1] >= 0xA0 && p[1] <= 0xBF && utf8_is_cont(p[2])) {
n = UTF8_THREE_BYTE_LEN;
} else if (c >= 0xE1 && c <= 0xEC && p + 2 < end && utf8_is_cont(p[1]) &&
utf8_is_cont(p[2])) {
n = UTF8_THREE_BYTE_LEN;
} else if (c == 0xED && p + 2 < end && p[1] >= 0x80 && p[1] <= 0x9F && utf8_is_cont(p[2])) {
n = UTF8_THREE_BYTE_LEN;
} else if (c >= 0xEE && c <= 0xEF && p + 2 < end && utf8_is_cont(p[1]) &&
utf8_is_cont(p[2])) {
n = UTF8_THREE_BYTE_LEN;
} else if (c == 0xF0 && p + UTF8_FOURTH_BYTE < end && p[1] >= 0x90 && p[1] <= 0xBF &&
utf8_is_cont(p[2]) && utf8_is_cont(p[UTF8_FOURTH_BYTE])) {
n = UTF8_FOUR_BYTE_LEN;
} else if (c >= 0xF1 && c <= 0xF3 && p + UTF8_FOURTH_BYTE < end && utf8_is_cont(p[1]) &&
utf8_is_cont(p[2]) && utf8_is_cont(p[UTF8_FOURTH_BYTE])) {
n = UTF8_FOUR_BYTE_LEN;
} else if (c == 0xF4 && p + UTF8_FOURTH_BYTE < end && p[1] >= 0x80 && p[1] <= 0x8F &&
utf8_is_cont(p[2]) && utf8_is_cont(p[UTF8_FOURTH_BYTE])) {
n = UTF8_FOUR_BYTE_LEN;
}

if (n > 0) {
memcpy(dst, p, n);
dst += n;
p += n;
} else {
*dst++ = 0xEF;
*dst++ = 0xBF;
*dst++ = 0xBD;
p++;
}
}
*dst = '\0';
return out;
}

/* Build an enriched snippet response for a resolved node. */
/* Add a string array to a JSON object (no-op if count == 0). */
static void add_string_array(yyjson_mut_doc *doc, yyjson_mut_val *obj, const char *key,
Expand Down Expand Up @@ -2877,7 +2946,13 @@ static char *build_snippet_response(cbm_mcp_server_t *srv, cbm_node_t *node,
yyjson_mut_obj_add_int(doc, root_obj, "end_line", end);

if (source) {
yyjson_mut_obj_add_str(doc, root_obj, "source", source);
char *safe_source = sanitize_utf8_lossy(source);
if (safe_source) {
yyjson_mut_obj_add_strcpy(doc, root_obj, "source", safe_source);
free(safe_source);
} else {
yyjson_mut_obj_add_str(doc, root_obj, "source", "(source not available)");
}
} else {
yyjson_mut_obj_add_str(doc, root_obj, "source", "(source not available)");
}
Expand Down
67 changes: 67 additions & 0 deletions tests/test_mcp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@
#include <yyjson/yyjson.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>

/* ══════════════════════════════════════════════════════════════════
* JSON-RPC PARSING
Expand Down Expand Up @@ -1291,6 +1292,31 @@ static char *call_snippet(cbm_mcp_server_t *srv, const char *args_json) {
return text;
}

static bool is_valid_json_response(const char *json) {
if (!json) {
return false;
}
yyjson_doc *doc = yyjson_read(json, strlen(json), 0);
if (!doc) {
return false;
}
yyjson_doc_free(doc);
return true;
}

static bool snippet_source_has_replacement(const char *json) {
yyjson_doc *doc = yyjson_read(json, strlen(json), 0);
if (!doc) {
return false;
}
yyjson_val *root = yyjson_doc_get_root(doc);
yyjson_val *source = yyjson_obj_get(root, "source");
const char *source_str = yyjson_get_str(source);
bool found = source_str && strstr(source_str, "\xEF\xBF\xBD");
yyjson_doc_free(doc);
return found;
}

/* ── TestSnippet_ExactQN ──────────────────────────────────────── */

TEST(snippet_exact_qn) {
Expand Down Expand Up @@ -1577,6 +1603,46 @@ TEST(snippet_include_neighbors_enabled) {
PASS();
}

/* ── TestSnippet_SourceInvalidUtf8 ────────────────────────────── */

TEST(snippet_source_invalid_utf8) {
char tmp[256];
cbm_mcp_server_t *srv = setup_snippet_server(tmp, sizeof(tmp));
ASSERT_NOT_NULL(srv);

char src_path[512];
snprintf(src_path, sizeof(src_path), "%s/project/main.go", tmp);
FILE *fp = fopen(src_path, "wb");
ASSERT_NOT_NULL(fp);
const unsigned char source[] = {
'p', 'a', 'c', 'k', 'a', 'g', 'e', ' ', 'm', 'a', 'i', 'n', '\n', '\n',
'f', 'u', 'n', 'c', ' ', 'H', 'a', 'n', 'd', 'l', 'e', 'R', 'e', 'q',
'u', 'e', 's', 't', '(', ')', ' ', 'e', 'r', 'r', 'o', 'r', ' ', '{',
'\n', '\t', '/', '/', ' ', 0xC0, 0xD4, 0xB7, 0xC2, '\n', '\t', 'r', 'e', 't',
'u', 'r', 'n', ' ', 'n', 'i', 'l', '\n', '}', '\n'};
ASSERT_EQ(fwrite(source, 1, sizeof(source), fp), sizeof(source));
ASSERT_EQ(fclose(fp), 0);

char *raw =
cbm_mcp_handle_tool(srv, "get_code_snippet",
"{\"qualified_name\":\"test-project.cmd.server.main.HandleRequest\","
"\"project\":\"test-project\"}");
ASSERT_TRUE(is_valid_json_response(raw));
char *resp = extract_text_content(raw);
ASSERT_NOT_NULL(resp);
ASSERT_TRUE(is_valid_json_response(resp));
ASSERT_NULL(strstr(resp, "\xC0\xD4"));
ASSERT_NOT_NULL(strstr(resp, "HandleRequest"));
ASSERT_NOT_NULL(strstr(resp, "return nil"));
ASSERT_TRUE(snippet_source_has_replacement(resp));

free(resp);
free(raw);
cbm_mcp_server_free(srv);
cleanup_snippet_dir(tmp);
PASS();
}

/* ══════════════════════════════════════════════════════════════════
* JSON-RPC PARSING — EDGE CASES
* ══════════════════════════════════════════════════════════════════ */
Expand Down Expand Up @@ -2129,5 +2195,6 @@ SUITE(mcp) {
RUN_TEST(snippet_auto_resolve_enabled);
RUN_TEST(snippet_include_neighbors_default);
RUN_TEST(snippet_include_neighbors_enabled);
RUN_TEST(snippet_source_invalid_utf8);
RUN_TEST(tool_bad_project_name_no_overflow_issue235);
}
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