feat: canister metadata command

CHANGELOG.adoc

@@ -21,6 +21,16 @@ After `dfx new <project>`, the canister names are:
 - `<project>_backend` (previously `<project>`)
 - `<project>_frontend` (previously `<project>_assets`)
 
+=== feat: new command: dfx canister metadata <canister> <name>
+
+For example, to query a canister's candid service definition: `dfx canister metadata hello_backend candid:service`
+
+=== refactor: deprecate /_/candid internal webserver
+
+The dfx internal webserver now only services the /_/candid endpoint.  This
+is now deprecated.  If you were using this to query candid definitions, you
+can instead use `dfx canister metadata`.
+
 === feat: Enable threshold ecdsa signature
 
 ECDSA signature signing is now enabled by default in new projects, or by running `dfx start --clean`.

docs/cli-reference/dfx-canister.md

@@ -26,6 +26,7 @@ For reference information and examples that illustrate using `dfx canister` comm
 | [`id`](#dfx-canister-id)                           | Displays the identifier of a canister.  |
 | [`info`](#dfx-canister-info)                       | Get the hash of a canister’s WASM module and its current controller.  |
 | [`install`](#dfx-canister-install)                 | Installs compiled code in a canister.  |
+| [`metadata`](#dfx-canister-metadata)               | Displays metadata in a canister.                  |
 | [`request-status`](#dfx-canister-request-status)   | Requests the status of a call to a canister.  |
 | [`send`](#dfx-canister-send)                       | Send a previously-signed message.  |
 | [`sign`](#dfx-canister-send)                       | Sign a canister call and generate message file.  |
@@ -506,6 +507,51 @@ With this setting, all of the canisters in the current projects are assigned a 5
 
 The default value for this option is 0—indicating that no specific allocation or scheduling is in effect. If all of your canisters use the default setting, processing occurs in a round-robin fashion.
 
+## dfx canister metadata
+
+Use the `dfx canister metadata` command to display metadata stored in a canister's WASM module.
+
+### Basic usage
+
+``` bash
+dfx canister metadata canister metadata-name
+```
+
+### Flags
+
+You can use the following optional flags with the `dfx canister metadata` command.
+
+| Flag              | Description                   |
+|-------------------|-------------------------------|
+| `-h`, `--help`    | Displays usage information.   |
+
+### Arguments
+
+You can use the following argument with the `dfx canister metadata` command.
+
+| Argument        | Description                                                                      |
+|-----------------|----------------------------------------------------------------------------------|
+| `canister`      | Specifies the name or id of the canister for which you want to display metadata. |
+| `metadata-name` | Specifies the name of the metadata which you want to display.                    |
+
+
+### Examples
+
+To display the candid service metadata for the `hello_world` canister, you can run the following command:
+
+``` bash
+dfx canister metadata hello_world candid:service
+```
+
+The command displays output similar to the following:
+
+```
+service : {
+  greet: (text) -> (text);
+}
+```
+
+
 ## dfx canister request-status
 
 Use the `dfx canister request-status` command to request the status of a specified call to a canister. This command requires you to specify the request identifier you received after invoking a method on the canister. The request identifier is an hexadecimal string starting with `0x`.

e2e/tests-dfx/build.bash

@@ -142,6 +142,10 @@ teardown() {
   dfx canister install --all
   assert_command dfx canister call custom fromQuery
   assert_command dfx canister call custom2 fromQuery
+
+  # dfx sets the candid:service metadata
+  dfx canister metadata custom candid:service >installed.did
+  assert_command diff main.did installed.did
 }
 
 @test "custom canister build script picks local executable first" {

e2e/tests-dfx/metadata.bash

@@ -0,0 +1,26 @@
+#!/usr/bin/env bats
+
+load ../utils/_
+
+setup() {
+    standard_setup
+
+    dfx_new
+}
+
+teardown() {
+    dfx_stop
+
+    standard_teardown
+}
+
+
+@test "can read canister metadata from replica" {
+    dfx_new hello
+    dfx_start
+
+    assert_command dfx deploy
+
+    dfx canister metadata hello_backend candid:service >metadata.txt
+    assert_command diff .dfx/local/canisters/hello_backend/hello_backend.did ./metadata.txt
+}

e2e/tests-dfx/rust.bash

@@ -23,6 +23,11 @@ teardown() {
     assert_command dfx canister install hello_backend
     assert_command dfx canister call hello_backend greet dfinity
     assert_match '("Hello, dfinity!")'
+
+    # dfx sets the candid:service metadata
+    dfx canister metadata hello_backend candid:service >installed.did
+    assert_command diff src/hello_backend/hello_backend.did installed.did
+
 }
 
 @test "rust canister can resolve dependencies" {

src/dfx/src/commands/canister/metadata.rs

@@ -0,0 +1,41 @@
+use crate::lib::error::DfxResult;
+use crate::lib::models::canister_id_store::CanisterIdStore;
+use crate::lib::root_key::fetch_root_key_if_needed;
+use crate::Environment;
+
+use anyhow::{anyhow, Context};
+use clap::Parser;
+use ic_types::Principal;
+use std::io::{stdout, Write};
+
+/// Sign a canister call and generate message file.
+#[derive(Parser)]
+pub struct CanisterMetadataOpts {
+    /// Specifies the name of the canister to call.
+    canister_name: String,
+
+    /// Specifies the name of the metadata to retrieve.
+    metadata_name: String,
+}
+
+pub async fn exec(env: &dyn Environment, opts: CanisterMetadataOpts) -> DfxResult {
+    let agent = env
+        .get_agent()
+        .ok_or_else(|| anyhow!("Cannot get HTTP client from environment."))?;
+
+    let callee_canister = opts.canister_name.as_str();
+    let canister_id_store = CanisterIdStore::for_env(env)?;
+
+    let canister_id = Principal::from_text(callee_canister)
+        .or_else(|_| canister_id_store.get(callee_canister))?;
+
+    fetch_root_key_if_needed(env).await?;
+    let metadata = agent
+        .read_state_canister_metadata(canister_id, &opts.metadata_name, false)
+        .await
+        .with_context(|| format!("Failed to read controllers of canister {}.", canister_id))?;
+
+    stdout().write_all(&metadata)?;
+
+    Ok(())
+}

src/dfx/src/commands/canister/mod.rs

@@ -13,6 +13,7 @@ mod deposit_cycles;
 mod id;
 mod info;
 mod install;
+mod metadata;
 mod request_status;
 mod send;
 mod sign;
@@ -51,6 +52,7 @@ enum SubCommand {
     Id(id::CanisterIdOpts),
     Info(info::InfoOpts),
     Install(install::CanisterInstallOpts),
+    Metadata(metadata::CanisterMetadataOpts),
     RequestStatus(request_status::RequestStatusOpts),
     Send(send::CanisterSendOpts),
     Sign(sign::CanisterSignOpts),
@@ -75,6 +77,7 @@ pub fn exec(env: &dyn Environment, opts: CanisterOpts) -> DfxResult {
             SubCommand::Id(v) => id::exec(&agent_env, v).await,
             SubCommand::Install(v) => install::exec(&agent_env, v, &call_sender).await,
             SubCommand::Info(v) => info::exec(&agent_env, v).await,
+            SubCommand::Metadata(v) => metadata::exec(&agent_env, v).await,
             SubCommand::RequestStatus(v) => request_status::exec(&agent_env, v).await,
             SubCommand::Send(v) => send::exec(&agent_env, v, &call_sender).await,
             SubCommand::Sign(v) => sign::exec(&agent_env, v, &call_sender).await,