Add Prometheus support

Dockerfile

@@ -10,6 +10,9 @@ RUN bun run build
 FROM oven/bun:1.2.19-alpine AS runner
 WORKDIR /app
 
+# Install tzdata for timezone support
+RUN apk add --no-cache tzdata
+
 COPY ./package.json ./bun.lock ./
 RUN bun install --frozen-lockfile --production --ignore-scripts --no-cache
 

README.md

@@ -204,10 +204,35 @@ These endpoints are designed to be compatible with the Anthropic Messages API.
 
 New endpoints for monitoring your Copilot usage and quotas.
 
-| Endpoint     | Method | Description                                                  |
-| ------------ | ------ | ------------------------------------------------------------ |
-| `GET /usage` | `GET`  | Get detailed Copilot usage statistics and quota information. |
-| `GET /token` | `GET`  | Get the current Copilot token being used by the API.         |
+| Endpoint      | Method | Description                                                  |
+| ------------- | ------ | ------------------------------------------------------------ |
+| `GET /usage`  | `GET`  | Get detailed Copilot usage statistics and quota information. |
+| `GET /token`  | `GET`  | Get the current Copilot token being used by the API.         |
+| `GET /metrics`| `GET`  | Prometheus metrics endpoint exposing token usage per model.  |
+
+### Prometheus Metrics
+
+The `/metrics` endpoint exposes Prometheus-compatible metrics for monitoring token usage:
+
+**Available Metrics:**
+- `copilot_api_tokens_in_total` - Total input tokens processed per model
+- `copilot_api_tokens_out_total` - Total output tokens generated per model  
+- `copilot_api_requests_total` - Total number of requests per model and endpoint
+
+Example metrics output:
+```
+# HELP copilot_api_tokens_in_total Total number of input tokens processed per model
+# TYPE copilot_api_tokens_in_total counter
+copilot_api_tokens_in_total{model="gpt-4o"} 1523
+
+# HELP copilot_api_tokens_out_total Total number of output tokens generated per model
+# TYPE copilot_api_tokens_out_total counter
+copilot_api_tokens_out_total{model="gpt-4o"} 342
+
+# HELP copilot_api_requests_total Total number of requests per model
+# TYPE copilot_api_requests_total counter
+copilot_api_requests_total{model="gpt-4o",endpoint="chat-completions"} 15
+```
 
 ## Example Usage
 

bun.lock

@@ -10,6 +10,7 @@
         "fetch-event-stream": "^0.1.5",
         "gpt-tokenizer": "^3.0.1",
         "hono": "^4.9.9",
+        "prom-client": "^15.1.3",
         "proxy-from-env": "^1.1.0",
         "srvx": "^0.8.9",
         "tiny-invariant": "^1.3.3",
@@ -114,6 +115,8 @@
 
     "@nodelib/fs.walk": ["@nodelib/fs.walk@1.2.8", "", { "dependencies": { "@nodelib/fs.scandir": "2.1.5", "fastq": "^1.6.0" } }, "sha512-oGB+UxlgWcgQkgwo8GcEGwemoTFt3FIO9ababBmaGwXIoBKZ+GTy0pP185beGg7Llih/NSHSV2XAs1lnznocSg=="],
 
+    "@opentelemetry/api": ["@opentelemetry/api@1.9.0", "", {}, "sha512-3giAOQvZiH5F9bMlMiv8+GSPMeqg0dbaeo58/0SlA9sxSqZhnUtxzX9/2FzyhS9sWQf5S0GJE0AKBrFqjpeYcg=="],
+
     "@oxc-project/types": ["@oxc-project/types@0.93.0", "", {}, "sha512-yNtwmWZIBtJsMr5TEfoZFDxIWV6OdScOpza/f5YxbqUMJk+j6QX3Cf3jgZShGEFYWQJ5j9mJ6jM0tZHu2J9Yrg=="],
 
     "@oxc-resolver/binding-android-arm-eabi": ["@oxc-resolver/binding-android-arm-eabi@11.9.0", "", { "os": "android", "cpu": "arm" }, "sha512-4AxaG6TkSBQ2FiC5oGZEJQ35DjsSfAbW6/AJauebq4EzIPVOIgDJCF4de+PvX/Xi9BkNw6VtJuMXJdWW97iEAA=="],
@@ -274,6 +277,8 @@
 
     "baseline-browser-mapping": ["baseline-browser-mapping@2.8.11", "", { "bin": { "baseline-browser-mapping": "dist/cli.js" } }, "sha512-i+sRXGhz4+QW8aACZ3+r1GAKMt0wlFpeA8M5rOQd0HEYw9zhDrlx9Wc8uQ0IdXakjJRthzglEwfB/yqIjO6iDg=="],
 
+    "bintrees": ["bintrees@1.0.2", "", {}, "sha512-VOMgTMwjAaUG580SXn3LacVgjurrbMme7ZZNYGSSV7mmtY6QQRh0Eg3pwIcntQ77DErK1L0NxkbetjcoXzVwKw=="],
+
     "birecord": ["birecord@0.1.1", "", {}, "sha512-VUpsf/qykW0heRlC8LooCq28Kxn3mAqKohhDG/49rrsQ1dT1CXyj/pgXS+5BSRzFTR/3DyIBOqQOrGyZOh71Aw=="],
 
     "birpc": ["birpc@2.6.1", "", {}, "sha512-LPnFhlDpdSH6FJhJyn4M0kFO7vtQ5iPw24FnG0y21q09xC7e8+1LeR31S1MAIrDAHp4m7aas4bEkTDTvMAtebQ=="],
@@ -776,6 +781,8 @@
 
     "pretty-ms": ["pretty-ms@9.3.0", "", { "dependencies": { "parse-ms": "^4.0.0" } }, "sha512-gjVS5hOP+M3wMm5nmNOucbIrqudzs9v/57bWRHQWLYklXqoXKrVfYW2W9+glfGsqtPgpiz5WwyEEB+ksXIx3gQ=="],
 
+    "prom-client": ["prom-client@15.1.3", "", { "dependencies": { "@opentelemetry/api": "^1.4.0", "tdigest": "^0.1.1" } }, "sha512-6ZiOBfCywsD4k1BN9IX0uZhF+tJkV8q8llP64G5Hajs4JOeVLPCwpPVcpXy3BwYiUGgyJzsJJQeOIv7+hDSq8g=="],
+
     "proxy-from-env": ["proxy-from-env@1.1.0", "", {}, "sha512-D+zkORCbA9f1tdWRK0RaCR3GPv50cMxcrz4X8k5LTSUD1Dkw47mKJEZQNunItRTkWwgtaUSo1RVFRIG9ZXiFYg=="],
 
     "punycode": ["punycode@2.3.1", "", {}, "sha512-vYt7UD1U9Wg6138shLtLOvdAu+8DsC/ilFtEVHcH+wydcSpNE20AfSOduf6MkRFahL5FY7X1oU7nKVZFtfq8Fg=="],
@@ -896,6 +903,8 @@
 
     "system-architecture": ["system-architecture@0.1.0", "", {}, "sha512-ulAk51I9UVUyJgxlv9M6lFot2WP3e7t8Kz9+IS6D4rVba1tR9kON+Ey69f+1R4Q8cd45Lod6a4IcJIxnzGc/zA=="],
 
+    "tdigest": ["tdigest@0.1.2", "", { "dependencies": { "bintrees": "1.0.2" } }, "sha512-+G0LLgjjo9BZX2MfdvPfH+MKLCrxlXSYec5DaPYP1fe6Iyhf0/fSmJ0bFiZ1F8BT6cGXl2LpltQptzjXKWEkKA=="],
+
     "tiny-invariant": ["tiny-invariant@1.3.3", "", {}, "sha512-+FbBPE1o9QAYvviau/qC5SE3caw21q3xkvWKBtja5vgqOWIHHJ3ioaq1VPfn/Szqctz2bU/oYeKd9/z5BL+PVg=="],
 
     "tinyexec": ["tinyexec@1.0.1", "", {}, "sha512-5uC6DDlmeqiOwCPmK9jMSdOuZTh8bU39Ys6yidB+UTt5hfZUPGAypSgFRiEp+jbi9qH40BLDvy85jIU88wKSqw=="],