cmd/abigen: support for reading solc output from stdin (#16683)

Allow the --abi flag to be given - to indicate that it should read the
ABI information from standard input. It expects to read the solc output
with the --combined-json flag providing bin, abi, userdoc, devdoc, and
metadata, and works very similarly to the internal invocation of solc,
except it allows external invocation of solc.

This facilitates integration with more complex solc invocations, such
as invocations that require path remapping or --allow-paths tweaks.

Simple usage example:

    solc --combined-json bin,abi,userdoc,devdoc,metadata *.sol | abigen --abi -

cmd/abigen/main.go

@@ -29,7 +29,7 @@ import (
 )
 
 var (
-	abiFlag = flag.String("abi", "", "Path to the Ethereum contract ABI json to bind")
+	abiFlag = flag.String("abi", "", "Path to the Ethereum contract ABI json to bind, - for STDIN")
 	binFlag = flag.String("bin", "", "Path to the Ethereum contract bytecode (generate deploy method)")
 	typFlag = flag.String("type", "", "Struct name for the binding (default = package name)")
 
@@ -75,17 +75,28 @@ func main() {
 		bins  []string
 		types []string
 	)
-	if *solFlag != "" {
+	if *solFlag != "" || *abiFlag == "-" {
 		// Generate the list of types to exclude from binding
 		exclude := make(map[string]bool)
 		for _, kind := range strings.Split(*excFlag, ",") {
 			exclude[strings.ToLower(kind)] = true
 		}
-		contracts, err := compiler.CompileSolidity(*solcFlag, *solFlag)
+
+		var contracts map[string]*compiler.Contract
+		var err error
+		if *solFlag != "" {
+			contracts, err = compiler.CompileSolidity(*solcFlag, *solFlag)
 			if err != nil {
 				fmt.Printf("Failed to build Solidity contract: %v\n", err)
 				os.Exit(-1)
 			}
+		} else {
+			contracts, err = contractsFromStdin()
+			if err != nil {
+				fmt.Printf("Failed to read input ABIs from STDIN: %v\n", err)
+				os.Exit(-1)
+			}
+		}
 		// Gather all non-excluded contract for binding
 		for name, contract := range contracts {
 			if exclude[strings.ToLower(name)] {
@@ -138,3 +149,12 @@ func main() {
 		os.Exit(-1)
 	}
 }
+
+func contractsFromStdin() (map[string]*compiler.Contract, error) {
+	bytes, err := ioutil.ReadAll(os.Stdin)
+	if err != nil {
+		return nil, err
+	}
+
+	return compiler.ParseCombinedJSON(bytes, "", "", "", "")
+}

common/compiler/solidity.go

@@ -31,11 +31,17 @@ import (
 
 var versionRegexp = regexp.MustCompile(`([0-9]+)\.([0-9]+)\.([0-9]+)`)
 
+// Contract contains information about a compiled contract, alongside its code.
 type Contract struct {
 	Code string       `json:"code"`
 	Info ContractInfo `json:"info"`
 }
 
+// ContractInfo contains information about a compiled contract, including access
+// to the ABI definition, user and developer docs, and metadata.
+//
+// Depending on the source, language version, compiler version, and compiler
+// options will provide information about how the contract was compiled.
 type ContractInfo struct {
 	Source          string      `json:"source"`
 	Language        string      `json:"language"`
@@ -142,8 +148,22 @@ func (s *Solidity) run(cmd *exec.Cmd, source string) (map[string]*Contract, erro
 	if err := cmd.Run(); err != nil {
 		return nil, fmt.Errorf("solc: %v\n%s", err, stderr.Bytes())
 	}
+
+	return ParseCombinedJSON(stdout.Bytes(), source, s.Version, s.Version, strings.Join(s.makeArgs(), " "))
+}
+
+// ParseCombinedJSON takes the direct output of a solc --combined-output run and
+// parses it into a map of string contract name to Contract structs. The
+// provided source, language and compiler version, and compiler options are all
+// passed through into the Contract structs.
+//
+// The solc output is expected to contain ABI, user docs, and dev docs.
+//
+// Returns an error if the JSON is malformed or missing data, or if the JSON
+// embedded within the JSON is malformed.
+func ParseCombinedJSON(combinedJSON []byte, source string, languageVersion string, compilerVersion string, compilerOptions string) (map[string]*Contract, error) {
 	var output solcOutput
-	if err := json.Unmarshal(stdout.Bytes(), &output); err != nil {
+	if err := json.Unmarshal(combinedJSON, &output); err != nil {
 		return nil, err
 	}
 
@@ -168,9 +188,9 @@ func (s *Solidity) run(cmd *exec.Cmd, source string) (map[string]*Contract, erro
 			Info: ContractInfo{
 				Source:          source,
 				Language:        "Solidity",
-				LanguageVersion: s.Version,
-				CompilerVersion: s.Version,
-				CompilerOptions: strings.Join(s.makeArgs(), " "),
+				LanguageVersion: languageVersion,
+				CompilerVersion: compilerVersion,
+				CompilerOptions: compilerOptions,
 				AbiDefinition:   abi,
 				UserDoc:         userdoc,
 				DeveloperDoc:    devdoc,