proxy-mcp

Instructions

Implementation Reference

• src/tools/devtools.ts:1283-1352 (handler)

  The handler implementation for the tool 'interceptor_chrome_devtools_get_network_field' which retrieves a full header field value from proxy-captured traffic.

    "interceptor_chrome_devtools_get_network_field",
    "Get one full header field value from proxy-captured traffic by field_id.",
    {
      devtools_session_id: z.string().describe("Session ID from interceptor_chrome_devtools_attach"),
      field_id: z.string().describe("field_id from interceptor_chrome_devtools_list_network_fields"),
      value_max_chars: z.number().optional().default(HARD_VALUE_CAP_CHARS)
        .describe(`Max characters for returned value (default: ${HARD_VALUE_CAP_CHARS})`),
    },
    async ({ devtools_session_id, field_id, value_max_chars }) => {
      try {
        const session = devToolsBridge.getSession(devtools_session_id);
        if (!session) {
          return { content: [{ type: "text", text: JSON.stringify({ status: "error", error: `DevTools session '${devtools_session_id}' not found.` }) }] };
        }
        const { targetId } = await ensureSessionTargetIsAlive(devtools_session_id);
  
        const parts = field_id.split(".");
        if (parts.length !== 4 || parts[0] !== "nf") {
          return { content: [{ type: "text", text: JSON.stringify({ status: "error", error: `Invalid field_id '${field_id}'` }) }] };
        }
        const exchangeId = parts[1];
        const dir = parts[2];
        const headerName = fromBase64UrlUtf8(parts[3]);
  
        const exchange = proxyManager.getExchange(exchangeId);
        if (!exchange) {
          return { content: [{ type: "text", text: JSON.stringify({ status: "error", error: `Exchange '${exchangeId}' not found in capture buffer.` }) }] };
        }
        if (exchange.timestamp < session.createdAt) {
          return { content: [{ type: "text", text: JSON.stringify({ status: "error", error: "field_id refers to an exchange older than this DevTools session." }) }] };
        }
  
        let value: string | null = null;
        if (dir === "request") {
          value = exchange.request.headers[headerName.toLowerCase()] ?? null;
        } else if (dir === "response") {
          value = exchange.response?.headers?.[headerName.toLowerCase()] ?? null;
        } else {
          return { content: [{ type: "text", text: JSON.stringify({ status: "error", error: `Invalid field direction '${dir}'` }) }] };
        }
  
        if (value === null) {
          return { content: [{ type: "text", text: JSON.stringify({ status: "error", error: `Header '${headerName}' not found on ${dir}.` }) }] };
        }
  
        const capped = capValue(value, Math.max(0, Math.min(HARD_VALUE_CAP_CHARS, Math.trunc(value_max_chars ?? HARD_VALUE_CAP_CHARS))));
  
        return {
          content: [{
            type: "text",
            text: truncateResult({
              status: "success",
              devtools_session_id,
              target_id: targetId,
              field_id,
              exchange_id: exchangeId,
              direction: dir,
              header_name: headerName,
              value: capped.value,
              value_length: capped.valueLength,
              value_truncated: capped.truncated,
              value_max_chars: capped.maxChars,
            }),
          }],
        };
      } catch (e) {
        return { content: [{ type: "text", text: JSON.stringify({ status: "error", error: errorToString(e) }) }] };
      }
    },
  );

• src/tools/devtools.ts:1283-1353 (registration)

  Registration of the 'interceptor_chrome_devtools_get_network_field' tool within the MCP server.

      "interceptor_chrome_devtools_get_network_field",
      "Get one full header field value from proxy-captured traffic by field_id.",
      {
        devtools_session_id: z.string().describe("Session ID from interceptor_chrome_devtools_attach"),
        field_id: z.string().describe("field_id from interceptor_chrome_devtools_list_network_fields"),
        value_max_chars: z.number().optional().default(HARD_VALUE_CAP_CHARS)
          .describe(`Max characters for returned value (default: ${HARD_VALUE_CAP_CHARS})`),
      },
      async ({ devtools_session_id, field_id, value_max_chars }) => {
        try {
          const session = devToolsBridge.getSession(devtools_session_id);
          if (!session) {
            return { content: [{ type: "text", text: JSON.stringify({ status: "error", error: `DevTools session '${devtools_session_id}' not found.` }) }] };
          }
          const { targetId } = await ensureSessionTargetIsAlive(devtools_session_id);
  
          const parts = field_id.split(".");
          if (parts.length !== 4 || parts[0] !== "nf") {
            return { content: [{ type: "text", text: JSON.stringify({ status: "error", error: `Invalid field_id '${field_id}'` }) }] };
          }
          const exchangeId = parts[1];
          const dir = parts[2];
          const headerName = fromBase64UrlUtf8(parts[3]);
  
          const exchange = proxyManager.getExchange(exchangeId);
          if (!exchange) {
            return { content: [{ type: "text", text: JSON.stringify({ status: "error", error: `Exchange '${exchangeId}' not found in capture buffer.` }) }] };
          }
          if (exchange.timestamp < session.createdAt) {
            return { content: [{ type: "text", text: JSON.stringify({ status: "error", error: "field_id refers to an exchange older than this DevTools session." }) }] };
          }
  
          let value: string | null = null;
          if (dir === "request") {
            value = exchange.request.headers[headerName.toLowerCase()] ?? null;
          } else if (dir === "response") {
            value = exchange.response?.headers?.[headerName.toLowerCase()] ?? null;
          } else {
            return { content: [{ type: "text", text: JSON.stringify({ status: "error", error: `Invalid field direction '${dir}'` }) }] };
          }
  
          if (value === null) {
            return { content: [{ type: "text", text: JSON.stringify({ status: "error", error: `Header '${headerName}' not found on ${dir}.` }) }] };
          }
  
          const capped = capValue(value, Math.max(0, Math.min(HARD_VALUE_CAP_CHARS, Math.trunc(value_max_chars ?? HARD_VALUE_CAP_CHARS))));
  
          return {
            content: [{
              type: "text",
              text: truncateResult({
                status: "success",
                devtools_session_id,
                target_id: targetId,
                field_id,
                exchange_id: exchangeId,
                direction: dir,
                header_name: headerName,
                value: capped.value,
                value_length: capped.valueLength,
                value_truncated: capped.truncated,
                value_max_chars: capped.maxChars,
              }),
            }],
          };
        } catch (e) {
          return { content: [{ type: "text", text: JSON.stringify({ status: "error", error: errorToString(e) }) }] };
        }
      },
    );
  }