doc: clarify which commands receive --chain, --fingerprint and --stdin

Bitcoin Core passes --chain and --fingerprint to every signer command
except enumerate, so mark them "(required except for enumerate)" and
name the current commands only as examples. Keep --stdin documented as
required for all commands so the interface stays flexible, noting that
Bitcoin Core currently only uses it for signtx.

Add the missing flags to the getdescriptors and displayaddress usage
examples and the corresponding doxygen comments, matching the order and
form of the actual invocations, add testnet4 to the chain name lists,
and drop the getaddressinfo implementation detail from the
walletdisplayaddress description.

doc/external-signer.md

@@ -84,13 +84,17 @@ Prerequisite knowledge:
 * [Output Descriptors](descriptors.md)
 * Partially Signed Bitcoin Transaction ([PSBT](psbt.md))
 
-### Flag `--chain <name>` (required)
+### Flag `--chain <name>` (required except for `enumerate`)
 
 With `<name>` one of `main`, `test`, `signet`, `regtest`, `testnet4`.
 
+Bitcoin Core passes this flag to commands that operate on a chain-specific signer, for example `getdescriptors`, `displayaddress` and `signtx`.
+
 ### Flag `--stdin` (required)
 
-Indicate that (sub)command should be received over stdin and results returned in response to that. `--stdin` is a global flag, it is not used for all subcommands.
+Indicate that (sub)command should be received over stdin and results returned in response to that. `--stdin` is a global flag, it is not specific to any subcommand.
+
+Bitcoin Core currently uses this flag for `signtx`.
 
 All subcommands SHOULD support both
 - being called as commandline arguments; or
@@ -107,11 +111,11 @@ Usage:
 
 Note: remember that shell-expansion is not available on _stdin_. Consequently, commands such as `signtx`, may write their arguments in either quoted or unquoted form.
 
-### Flag `--fingerprint <fingerprint>` (required)
+### Flag `--fingerprint <fingerprint>` (required except for `enumerate`)
 
 With `<fingerprint>` being the hexadecimal 8-symbol identifier for a wallet.
 
-Commands will specify a fingerprint as an identifier for external-signer wallet.
+Bitcoin Core passes this flag to commands that operate on a specific external-signer wallet, for example `getdescriptors`, `displayaddress` and `signtx`.
 
 ### `enumerate` (required)
 
@@ -155,14 +159,13 @@ The command MAY complain if `--chain` is set to a test-network, but any of the B
 Usage:
 
 ```sh
-<cmd> --fingerprint=<fingerprint> getdescriptors <account>
-<xpub>
+<cmd> --fingerprint <fingerprint> --chain <name> getdescriptors --account <account>
 ```
 
 Returns descriptors supported by the device. Example:
 
 ```sh
-<cmd> --fingerprint=00000000 getdescriptors
+<cmd> --fingerprint 00000000 --chain main getdescriptors --account 0
 ```
 
 ```
@@ -184,13 +187,13 @@ Returns descriptors supported by the device. Example:
 
 Usage:
 ```sh
-<cmd> --fingerprint=<fingerprint> displayaddress --desc <descriptor>
+<cmd> --fingerprint <fingerprint> --chain <name> displayaddress --desc <descriptor>
 ```
 
 Example, display the first native SegWit receive address on Testnet:
 
 ```sh
-<cmd> --chain test --fingerprint=00000000 displayaddress --desc "wpkh([00000000/84h/1h/0h]tpubDDUZ..../0/0)"
+<cmd> --fingerprint 00000000 --chain test displayaddress --desc "wpkh([00000000/84h/1h/0h]tpubDDUZ..../0/0)"
 ```
 
 The command MUST be able to figure out the address type from the descriptor.
@@ -212,10 +215,10 @@ Wallet operations that need a signer (`createwallet`, `walletdisplayaddress` and
 
 The `createwallet` RPC calls:
 
-* `<cmd> --chain <name> --fingerprint=00000000 getdescriptors --account 0`
+* `<cmd> --fingerprint 00000000 --chain <name> getdescriptors --account 0`
 
 It then imports descriptors for all supported address types, in a BIP44/49/84/86 compatible manner.
 
-The `walletdisplayaddress` RPC reuses some code from `getaddressinfo` on the provided address and obtains the inferred descriptor. It then calls `<cmd> --fingerprint=00000000 displayaddress --desc=<descriptor>`.
+The `walletdisplayaddress` RPC obtains the inferred descriptor for the provided address. It then calls `<cmd> --fingerprint 00000000 --chain <name> displayaddress --desc <descriptor>`.
 
 For external-signer wallets, spending uses `send` or `sendall`, and fee-bumping uses `bumpfee`. Bitcoin Core builds a PSBT, adds key origin information, checks whether any input key origin fingerprint matches the signer, calls `<cmd> --stdin --fingerprint 00000000 --chain <name>`, and sends `signtx <psbt>` over stdin. If signatures are sufficient, it finalizes the transaction and, for broadcasting RPCs, broadcasts it. If signing cannot complete, the call fails with an error. For manual fee-bumping, use `psbtbumpfee` to obtain a PSBT for signing.

src/external_signer.h

@@ -29,7 +29,7 @@ private:
 public:
     //! @param[in] command      the command which handles interaction with the external signer
     //! @param[in] fingerprint  master key fingerprint of the signer
-    //! @param[in] chain        "main", "test", "regtest" or "signet"
+    //! @param[in] chain        "main", "test", "signet", "regtest" or "testnet4"
     //! @param[in] name         device name
     ExternalSigner(std::vector<std::string> command, std::string chain, std::string fingerprint, std::string name);
 
@@ -42,17 +42,19 @@ public:
     //! Obtain a list of signers. Calls `<command> enumerate`.
     //! @param[in]              command the command which handles interaction with the external signer
     //! @param[in,out] signers  vector to which new signers (with a unique master key fingerprint) are added
-    //! @param chain            "main", "test", "regtest" or "signet"
+    //! @param chain            "main", "test", "signet", "regtest" or "testnet4"
     //! @returns success
     static bool Enumerate(const std::string& command, std::vector<ExternalSigner>& signers, const std::string& chain);
 
-    //! Display address on the device. Calls `<command> displayaddress --desc <descriptor>`.
+    //! Display address on the device. Calls `<command> --fingerprint <fingerprint> --chain <chain>
+    //! displayaddress --desc <descriptor>`.
     //! @param[in] descriptor Descriptor specifying which address to display.
     //!            Must include a public key or xpub, as well as key origin.
     UniValue DisplayAddress(const std::string& descriptor) const;
 
     //! Get receive and change Descriptor(s) from device for a given account.
-    //! Calls `<command> getdescriptors --account <account>`
+    //! Calls `<command> --fingerprint <fingerprint> --chain <chain> getdescriptors
+    //! --account <account>`.
     //! @param[in] account  which BIP32 account to use (e.g. `m/44'/0'/account'`)
     //! @returns see doc/external-signer.md
     UniValue GetDescriptors(int account);