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feat(server): add /v1/messages/count_tokens endpoint #90

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feat(server): add /v1/messages/count_tokens endpoint #90

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23 changes: 21 additions & 2 deletions ds4_server.c
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Original file line number Diff line number Diff line change
Expand Up @@ -7701,8 +7701,19 @@ static void *client_main(void *arg) {
request req;
char err[160];
bool ok = false;
bool count_tokens_only = false;
const int ctx_size = ds4_session_ctx(s->session);
if (!strcmp(hr.method, "POST") && !strcmp(hr.path, "/v1/messages")) {
if (!strcmp(hr.method, "POST") && !strcmp(hr.path, "/v1/messages/count_tokens")) {
/* Anthropic's count_tokens endpoint takes the same request shape as
* /v1/messages but only returns the prompt token total — no inference
* runs, so we short-circuit before the worker queue. Pass a NULL
* server so parse_anthropic_request skips the tool-memory and
* KV-cache lookups it would normally do; both helpers no-op cleanly
* on NULL, leaving shared state untouched for a read-only count. */
ok = parse_anthropic_request(s->engine, NULL, hr.body, s->default_tokens,
ctx_size, &req, err, sizeof(err));
if (ok) count_tokens_only = true;
} else if (!strcmp(hr.method, "POST") && !strcmp(hr.path, "/v1/messages")) {
ok = parse_anthropic_request(s->engine, s, hr.body, s->default_tokens,
ctx_size, &req, err, sizeof(err));
} else if (!strcmp(hr.method, "POST") && !strcmp(hr.path, "/v1/chat/completions")) {
Expand All @@ -7723,6 +7734,14 @@ static void *client_main(void *arg) {
goto done;
}

if (count_tokens_only) {
char body[64];
snprintf(body, sizeof(body), "{\"input_tokens\":%d}", req.prompt.len);
http_response(fd, 200, "application/json", body);
request_free(&req);
goto done;
}

set_client_socket_nonblocking(fd);
job j;
memset(&j, 0, sizeof(j));
Expand Down Expand Up @@ -7957,7 +7976,7 @@ static void usage(FILE *fp) {
" ./ds4-server --ctx 100000 --kv-disk-dir /tmp/ds4-kv --kv-disk-space-mb 8192\n"
"\n"
"Notes:\n"
" Use /v1/chat/completions, /v1/completions, or /v1/messages.\n"
" Use /v1/chat/completions, /v1/completions, /v1/messages, or /v1/messages/count_tokens.\n"
" Larger --ctx values allocate more KV memory at startup; the startup log prints the estimate.\n"
" Disk KV caching is best for agents that resend long prompts with stable prefixes.\n"
"\n"
Expand Down