common/compiler: simplify solc wrapper

Support for legacy version 0.9.x is gone. The compiler version is no
longer cached. Compilation results (and the version) are read directly
from stdout using the --combined-json flag. As a workaround for
ethereum/solidity#651, source code is written to a temporary file before
compilation.

Integration of solc in package ethapi and cmd/abigen is now much simpler
because the compiler wrapper is no longer passed around as a pointer.

Fixes #2806, accidentally

8 files changed, 225 insertions, 254 deletions

diff --git a/cmd/abigen/main.go b/cmd/abigen/main.go
index f36391351..9c9ab6d31 100644
--- a/cmd/abigen/main.go
+++ b/cmd/abigen/main.go
@@ -68,18 +68,7 @@ func main() {
 		for _, kind := range strings.Split(*excFlag, ",") {
 			exclude[strings.ToLower(kind)] = true
 		}
-		// Build the Solidity source into bindable components
-		solc, err := compiler.New(*solcFlag)
-		if err != nil {
-			fmt.Printf("Failed to locate Solidity compiler: %v\n", err)
-			os.Exit(-1)
-		}
-		source, err := ioutil.ReadFile(*solFlag)
-		if err != nil {
-			fmt.Printf("Failed to read Soldity source code: %v\n", err)
-			os.Exit(-1)
-		}
-		contracts, err := solc.Compile(string(source))
+		contracts, err := compiler.CompileSolidity(*solcFlag, *solFlag)
 		if err != nil {
 			fmt.Printf("Failed to build Solidity contract: %v\n", err)
 			os.Exit(-1)
diff --git a/common/compiler/solidity.go b/common/compiler/solidity.go
index 6a5bfecd8..b682107d9 100644
--- a/common/compiler/solidity.go
+++ b/common/compiler/solidity.go
@@ -14,6 +14,7 @@
 // You should have received a copy of the GNU Lesser General Public License
 // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
 
+// Package compiler wraps the Solidity compiler executable (solc).
 package compiler
 
 import (
@@ -21,42 +22,23 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"os"
 	"os/exec"
-	"path/filepath"
 	"regexp"
 	"strings"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/crypto"
-	"github.com/ethereum/go-ethereum/logger"
-	"github.com/ethereum/go-ethereum/logger/glog"
 )
 
 var (
 	versionRegexp = regexp.MustCompile("[0-9]+\\.[0-9]+\\.[0-9]+")
-	legacyRegexp  = regexp.MustCompile("0\\.(9\\..*|1\\.[01])")
-	paramsLegacy  = []string{
-		"--binary",       // Request to output the contract in binary (hexadecimal).
-		"file",           //
-		"--json-abi",     // Request to output the contract's JSON ABI interface.
-		"file",           //
-		"--natspec-user", // Request to output the contract's Natspec user documentation.
-		"file",           //
-		"--natspec-dev",  // Request to output the contract's Natspec developer documentation.
-		"file",
-		"--add-std",
-		"1",
-	}
-	paramsNew = []string{
-		"--bin",      // Request to output the contract in binary (hexadecimal).
-		"--abi",      // Request to output the contract's JSON ABI interface.
-		"--userdoc",  // Request to output the contract's Natspec user documentation.
-		"--devdoc",   // Request to output the contract's Natspec developer documentation.
+	solcParams    = []string{
+		"--combined-json", "bin,abi,userdoc,devdoc",
 		"--add-std",  // include standard lib contracts
 		"--optimize", // code optimizer switched on
-		"-o",         // output directory
 	}
 )
 
@@ -76,135 +58,112 @@ type ContractInfo struct {
 	DeveloperDoc    interface{} `json:"developerDoc"`
 }
 
+// Solidity contains information about the solidity compiler.
 type Solidity struct {
-	solcPath    string
-	version     string
-	fullVersion string
-	legacy      bool
+	Path, Version, FullVersion string
 }
 
-func New(solcPath string) (sol *Solidity, err error) {
-	// set default solc
-	if len(solcPath) == 0 {
-		solcPath = "solc"
-	}
-	solcPath, err = exec.LookPath(solcPath)
-	if err != nil {
-		return
-	}
+// --combined-output format
+type solcOutput struct {
+	Contracts map[string]struct{ Bin, Abi, Devdoc, Userdoc string }
+	Version   string
+}
 
-	cmd := exec.Command(solcPath, "--version")
+// SolidityVersion runs solc and parses its version output.
+func SolidityVersion(solc string) (*Solidity, error) {
+	if solc == "" {
+		solc = "solc"
+	}
 	var out bytes.Buffer
+	cmd := exec.Command(solc, "--version")
 	cmd.Stdout = &out
-	err = cmd.Run()
-	if err != nil {
-		return
+	if err := cmd.Run(); err != nil {
+		return nil, err
 	}
-
-	fullVersion := out.String()
-	version := versionRegexp.FindString(fullVersion)
-	legacy := legacyRegexp.MatchString(version)
-
-	sol = &Solidity{
-		solcPath:    solcPath,
-		version:     version,
-		fullVersion: fullVersion,
-		legacy:      legacy,
+	s := &Solidity{
+		Path:        cmd.Path,
+		FullVersion: out.String(),
+		Version:     versionRegexp.FindString(out.String()),
 	}
-	glog.V(logger.Info).Infoln(sol.Info())
-	return
-}
-
-func (sol *Solidity) Info() string {
-	return fmt.Sprintf("%s\npath: %s", sol.fullVersion, sol.solcPath)
-}
-
-func (sol *Solidity) Version() string {
-	return sol.version
+	return s, nil
 }
 
-// Compile builds and returns all the contracts contained within a source string.
-func (sol *Solidity) Compile(source string) (map[string]*Contract, error) {
-	// Short circuit if no source code was specified
+// CompileSolidityString builds and returns all the contracts contained within a source string.
+func CompileSolidityString(solc, source string) (map[string]*Contract, error) {
 	if len(source) == 0 {
 		return nil, errors.New("solc: empty source string")
 	}
-	// Create a safe place to dump compilation output
-	wd, err := ioutil.TempDir("", "solc")
+	if solc == "" {
+		solc = "solc"
+	}
+	// Write source to a temporary file. Compiling stdin used to be supported
+	// but seems to produce an exception with solc 0.3.5.
+	infile, err := ioutil.TempFile("", "geth-compile-solidity")
 	if err != nil {
-		return nil, fmt.Errorf("solc: failed to create temporary build folder: %v", err)
+		return nil, err
+	}
+	defer os.Remove(infile.Name())
+	if _, err := io.WriteString(infile, source); err != nil {
+		return nil, err
+	}
+	if err := infile.Close(); err != nil {
+		return nil, err
 	}
-	defer os.RemoveAll(wd)
 
-	// Assemble the compiler command, change to the temp folder and capture any errors
-	stderr := new(bytes.Buffer)
+	return CompileSolidity(solc, infile.Name())
+}
 
-	var params []string
-	if sol.legacy {
-		params = paramsLegacy
-	} else {
-		params = paramsNew
-		params = append(params, wd)
+// CompileSolidity compiles all given Solidity source files.
+func CompileSolidity(solc string, sourcefiles ...string) (map[string]*Contract, error) {
+	if len(sourcefiles) == 0 {
+		return nil, errors.New("solc: no source ")
+	}
+	source, err := slurpFiles(sourcefiles)
+	if err != nil {
+		return nil, err
+	}
+	if solc == "" {
+		solc = "solc"
 	}
-	compilerOptions := strings.Join(params, " ")
-
-	cmd := exec.Command(sol.solcPath, params...)
-	cmd.Stdin = strings.NewReader(source)
-	cmd.Stderr = stderr
 
+	var stderr, stdout bytes.Buffer
+	args := append(solcParams, "--")
+	cmd := exec.Command(solc, append(args, sourcefiles...)...)
+	cmd.Stderr = &stderr
+	cmd.Stdout = &stdout
 	if err := cmd.Run(); err != nil {
-		return nil, fmt.Errorf("solc: %v\n%s", err, string(stderr.Bytes()))
+		return nil, fmt.Errorf("solc: %v\n%s", err, stderr.Bytes())
 	}
-	// Sanity check that something was actually built
-	matches, _ := filepath.Glob(filepath.Join(wd, "*.bin*"))
-	if len(matches) < 1 {
-		return nil, fmt.Errorf("solc: no build results found")
+	var output solcOutput
+	if err := json.Unmarshal(stdout.Bytes(), &output); err != nil {
+		return nil, err
 	}
-	// Compilation succeeded, assemble and return the contracts
-	contracts := make(map[string]*Contract)
-	for _, path := range matches {
-		_, file := filepath.Split(path)
-		base := strings.Split(file, ".")[0]
-
-		// Parse the individual compilation results (code binary, ABI definitions, user and dev docs)
-		var binary []byte
-		binext := ".bin"
-		if sol.legacy {
-			binext = ".binary"
-		}
-		if binary, err = ioutil.ReadFile(filepath.Join(wd, base+binext)); err != nil {
-			return nil, fmt.Errorf("solc: error reading compiler output for code: %v", err)
-		}
+	shortVersion := versionRegexp.FindString(output.Version)
 
+	// Compilation succeeded, assemble and return the contracts.
+	contracts := make(map[string]*Contract)
+	for name, info := range output.Contracts {
+		// Parse the individual compilation results.
 		var abi interface{}
-		if blob, err := ioutil.ReadFile(filepath.Join(wd, base+".abi")); err != nil {
-			return nil, fmt.Errorf("solc: error reading abi definition: %v", err)
-		} else if err = json.Unmarshal(blob, &abi); err != nil {
-			return nil, fmt.Errorf("solc: error parsing abi definition: %v", err)
+		if err := json.Unmarshal([]byte(info.Abi), &abi); err != nil {
+			return nil, fmt.Errorf("solc: error reading abi definition (%v)", err)
 		}
-
 		var userdoc interface{}
-		if blob, err := ioutil.ReadFile(filepath.Join(wd, base+".docuser")); err != nil {
+		if err := json.Unmarshal([]byte(info.Userdoc), &userdoc); err != nil {
 			return nil, fmt.Errorf("solc: error reading user doc: %v", err)
-		} else if err = json.Unmarshal(blob, &userdoc); err != nil {
-			return nil, fmt.Errorf("solc: error parsing user doc: %v", err)
 		}
-
 		var devdoc interface{}
-		if blob, err := ioutil.ReadFile(filepath.Join(wd, base+".docdev")); err != nil {
+		if err := json.Unmarshal([]byte(info.Devdoc), &devdoc); err != nil {
 			return nil, fmt.Errorf("solc: error reading dev doc: %v", err)
-		} else if err = json.Unmarshal(blob, &devdoc); err != nil {
-			return nil, fmt.Errorf("solc: error parsing dev doc: %v", err)
 		}
-		// Assemble the final contract
-		contracts[base] = &Contract{
-			Code: "0x" + string(binary),
+		contracts[name] = &Contract{
+			Code: "0x" + info.Bin,
 			Info: ContractInfo{
 				Source:          source,
 				Language:        "Solidity",
-				LanguageVersion: sol.version,
-				CompilerVersion: sol.version,
-				CompilerOptions: compilerOptions,
+				LanguageVersion: shortVersion,
+				CompilerVersion: shortVersion,
+				CompilerOptions: strings.Join(solcParams, " "),
 				AbiDefinition:   abi,
 				UserDoc:         userdoc,
 				DeveloperDoc:    devdoc,
@@ -214,12 +173,24 @@ func (sol *Solidity) Compile(source string) (map[string]*Contract, error) {
 	return contracts, nil
 }
 
-func SaveInfo(info *ContractInfo, filename string) (contenthash common.Hash, err error) {
+func slurpFiles(files []string) (string, error) {
+	var concat bytes.Buffer
+	for _, file := range files {
+		content, err := ioutil.ReadFile(file)
+		if err != nil {
+			return "", err
+		}
+		concat.Write(content)
+	}
+	return concat.String(), nil
+}
+
+// SaveInfo serializes info to the given file and returns its Keccak256 hash.
+func SaveInfo(info *ContractInfo, filename string) (common.Hash, error) {
 	infojson, err := json.Marshal(info)
 	if err != nil {
-		return
+		return common.Hash{}, err
 	}
-	contenthash = common.BytesToHash(crypto.Keccak256(infojson))
-	err = ioutil.WriteFile(filename, infojson, 0600)
-	return
+	contenthash := common.BytesToHash(crypto.Keccak256(infojson))
+	return contenthash, ioutil.WriteFile(filename, infojson, 0600)
 }
diff --git a/common/compiler/solidity_test.go b/common/compiler/solidity_test.go
index 7109b1ec4..e4d96bd01 100644
--- a/common/compiler/solidity_test.go
+++ b/common/compiler/solidity_test.go
@@ -26,10 +26,9 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 )
 
-const solcVersion = "0.1.1"
-
-var (
-	source = `
+const (
+	supportedSolcVersion = "0.3.5"
+	testSource           = `
 contract test {
    /// @notice Will multiply ` + "`a`" + ` by 7.
    function multiply(uint a) returns(uint d) {
@@ -37,61 +36,57 @@ contract test {
    }
 }
 `
-	code = "0x6060604052606d8060116000396000f30060606040526000357c010000000000000000000000000000000000000000000000000000000090048063c6888fa1146037576035565b005b6046600480359060200150605c565b6040518082815260200191505060405180910390f35b60006007820290506068565b91905056"
-	info = `{"source":"\ncontract test {\n   /// @notice Will multiply ` + "`a`" + ` by 7.\n   function multiply(uint a) returns(uint d) {\n       return a * 7;\n   }\n}\n","language":"Solidity","languageVersion":"0.1.1","compilerVersion":"0.1.1","compilerOptions":"--binary file --json-abi file --natspec-user file --natspec-dev file --add-std 1","abiDefinition":[{"constant":false,"inputs":[{"name":"a","type":"uint256"}],"name":"multiply","outputs":[{"name":"d","type":"uint256"}],"type":"function"}],"userDoc":{"methods":{"multiply(uint256)":{"notice":"Will multiply ` + "`a`" + ` by 7."}}},"developerDoc":{"methods":{}}}`
-
-	infohash = common.HexToHash("0x9f3803735e7f16120c5a140ab3f02121fd3533a9655c69b33a10e78752cc49b0")
+	testCode = "0x6060604052602a8060106000396000f3606060405260e060020a6000350463c6888fa18114601a575b005b6007600435026060908152602090f3"
+	testInfo = `{"source":"\ncontract test {\n   /// @notice Will multiply ` + "`a`" + ` by 7.\n   function multiply(uint a) returns(uint d) {\n       return a * 7;\n   }\n}\n","language":"Solidity","languageVersion":"0.1.1","compilerVersion":"0.1.1","compilerOptions":"--binary file --json-abi file --natspec-user file --natspec-dev file --add-std 1","abiDefinition":[{"constant":false,"inputs":[{"name":"a","type":"uint256"}],"name":"multiply","outputs":[{"name":"d","type":"uint256"}],"type":"function"}],"userDoc":{"methods":{"multiply(uint256)":{"notice":"Will multiply ` + "`a`" + ` by 7."}}},"developerDoc":{"methods":{}}}`
 )
 
-func TestCompiler(t *testing.T) {
-	sol, err := New("")
+func skipUnsupported(t *testing.T) {
+	sol, err := SolidityVersion("")
 	if err != nil {
-		t.Skipf("solc not found: %v", err)
-	} else if sol.Version() != solcVersion {
-		t.Skipf("WARNING: a newer version of solc found (%v, expect %v)", sol.Version(), solcVersion)
-	}
-	contracts, err := sol.Compile(source)
-	if err != nil {
-		t.Errorf("error compiling source. result %v: %v", contracts, err)
+		t.Skip(err)
 		return
 	}
+	if sol.Version != supportedSolcVersion {
+		t.Skipf("unsupported version of solc found (%v, expect %v)", sol.Version, supportedSolcVersion)
+	}
+}
 
+func TestCompiler(t *testing.T) {
+	skipUnsupported(t)
+	contracts, err := CompileSolidityString("", testSource)
+	if err != nil {
+		t.Fatalf("error compiling source. result %v: %v", contracts, err)
+	}
 	if len(contracts) != 1 {
 		t.Errorf("one contract expected, got %d", len(contracts))
 	}
-
-	if contracts["test"].Code != code {
-		t.Errorf("wrong code, expected\n%s, got\n%s", code, contracts["test"].Code)
+	c, ok := contracts["test"]
+	if !ok {
+		t.Fatal("info for contract 'test' not present in result")
+	}
+	if c.Code != testCode {
+		t.Errorf("wrong code: expected\n%s, got\n%s", testCode, c.Code)
+	}
+	if c.Info.Source != testSource {
+		t.Error("wrong source")
+	}
+	if c.Info.CompilerVersion != supportedSolcVersion {
+		t.Errorf("wrong version: expected %q, got %q", supportedSolcVersion, c.Info.CompilerVersion)
 	}
-
 }
 
 func TestCompileError(t *testing.T) {
-	sol, err := New("")
-	if err != nil || sol.version != solcVersion {
-		t.Skip("solc not found: skip")
-	} else if sol.Version() != solcVersion {
-		t.Skip("WARNING: skipping due to a newer version of solc found (%v, expect %v)", sol.Version(), solcVersion)
-	}
-	contracts, err := sol.Compile(source[2:])
+	skipUnsupported(t)
+	contracts, err := CompileSolidityString("", testSource[4:])
 	if err == nil {
 		t.Errorf("error expected compiling source. got none. result %v", contracts)
-		return
-	}
-}
-
-func TestNoCompiler(t *testing.T) {
-	_, err := New("/path/to/solc")
-	if err != nil {
-		t.Logf("solidity quits with error: %v", err)
-	} else {
-		t.Errorf("no solc installed, but got no error")
 	}
+	t.Logf("error: %v", err)
 }
 
 func TestSaveInfo(t *testing.T) {
 	var cinfo ContractInfo
-	err := json.Unmarshal([]byte(info), &cinfo)
+	err := json.Unmarshal([]byte(testInfo), &cinfo)
 	if err != nil {
 		t.Errorf("%v", err)
 	}
@@ -105,10 +100,11 @@ func TestSaveInfo(t *testing.T) {
 	if err != nil {
 		t.Errorf("error reading '%v': %v", filename, err)
 	}
-	if string(got) != info {
-		t.Errorf("incorrect info.json extracted, expected:\n%s\ngot\n%s", info, string(got))
+	if string(got) != testInfo {
+		t.Errorf("incorrect info.json extracted, expected:\n%s\ngot\n%s", testInfo, string(got))
 	}
-	if cinfohash != infohash {
-		t.Errorf("content hash for info is incorrect. expected %v, got %v", infohash.Hex(), cinfohash.Hex())
+	wantHash := common.HexToHash("0x9f3803735e7f16120c5a140ab3f02121fd3533a9655c69b33a10e78752cc49b0")
+	if cinfohash != wantHash {
+		t.Errorf("content hash for info is incorrect. expected %v, got %v", wantHash.Hex(), cinfohash.Hex())
 	}
 }
diff --git a/eth/backend.go b/eth/backend.go
index 22388ddb5..e1d123a02 100644
--- a/eth/backend.go
+++ b/eth/backend.go
@@ -31,7 +31,6 @@ import (
 	"github.com/ethereum/ethash"
 	"github.com/ethereum/go-ethereum/accounts"
 	"github.com/ethereum/go-ethereum/common"
-	"github.com/ethereum/go-ethereum/common/compiler"
 	"github.com/ethereum/go-ethereum/common/httpclient"
 	"github.com/ethereum/go-ethereum/common/registrar/ethreg"
 	"github.com/ethereum/go-ethereum/core"
@@ -130,7 +129,6 @@ type Ethereum struct {
 	autodagquit  chan bool
 	etherbase    common.Address
 	solcPath     string
-	solc         *compiler.Solidity
 
 	NatSpec       bool
 	PowTest       bool
@@ -291,7 +289,7 @@ func CreatePoW(config *Config) (*ethash.Ethash, error) {
 // APIs returns the collection of RPC services the ethereum package offers.
 // NOTE, some of these services probably need to be moved to somewhere else.
 func (s *Ethereum) APIs() []rpc.API {
-	return append(ethapi.GetAPIs(s.apiBackend, &s.solcPath, &s.solc), []rpc.API{
+	return append(ethapi.GetAPIs(s.apiBackend, s.solcPath), []rpc.API{
 		{
 			Namespace: "eth",
 			Version:   "1.0",
diff --git a/eth/bind.go b/eth/bind.go
index c1366464f..bf7a7fb53 100644
--- a/eth/bind.go
+++ b/eth/bind.go
@@ -44,7 +44,7 @@ type ContractBackend struct {
 // Etheruem object.
 func NewContractBackend(eth *Ethereum) *ContractBackend {
 	return &ContractBackend{
-		eapi:  ethapi.NewPublicEthereumAPI(eth.apiBackend, nil, nil),
+		eapi:  ethapi.NewPublicEthereumAPI(eth.apiBackend),
 		bcapi: ethapi.NewPublicBlockChainAPI(eth.apiBackend),
 		txapi: ethapi.NewPublicTransactionPoolAPI(eth.apiBackend),
 	}
diff --git a/internal/ethapi/api.go b/internal/ethapi/api.go
index 88bacc45b..ac9e2151d 100644
--- a/internal/ethapi/api.go
+++ b/internal/ethapi/api.go
@@ -20,7 +20,6 @@ import (
 	"bytes"
 	"encoding/hex"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"math/big"
 	"strings"
@@ -30,7 +29,6 @@ import (
 	"github.com/ethereum/ethash"
 	"github.com/ethereum/go-ethereum/accounts"
 	"github.com/ethereum/go-ethereum/common"
-	"github.com/ethereum/go-ethereum/common/compiler"
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/core/vm"
@@ -50,14 +48,12 @@ const defaultGas = uint64(90000)
 // PublicEthereumAPI provides an API to access Ethereum related information.
 // It offers only methods that operate on public data that is freely available to anyone.
 type PublicEthereumAPI struct {
-	b        Backend
-	solcPath *string
-	solc     **compiler.Solidity
+	b Backend
 }
 
 // NewPublicEthereumAPI creates a new Etheruem protocol API.
-func NewPublicEthereumAPI(b Backend, solcPath *string, solc **compiler.Solidity) *PublicEthereumAPI {
-	return &PublicEthereumAPI{b, solcPath, solc}
+func NewPublicEthereumAPI(b Backend) *PublicEthereumAPI {
+	return &PublicEthereumAPI{b}
 }
 
 // GasPrice returns a suggestion for a gas price.
@@ -65,39 +61,6 @@ func (s *PublicEthereumAPI) GasPrice(ctx context.Context) (*big.Int, error) {
 	return s.b.SuggestPrice(ctx)
 }
 
-func (s *PublicEthereumAPI) getSolc() (*compiler.Solidity, error) {
-	var err error
-	solc := *s.solc
-	if solc == nil {
-		solc, err = compiler.New(*s.solcPath)
-	}
-	return solc, err
-}
-
-// GetCompilers returns the collection of available smart contract compilers
-func (s *PublicEthereumAPI) GetCompilers() ([]string, error) {
-	solc, err := s.getSolc()
-	if err == nil && solc != nil {
-		return []string{"Solidity"}, nil
-	}
-
-	return []string{}, nil
-}
-
-// CompileSolidity compiles the given solidity source
-func (s *PublicEthereumAPI) CompileSolidity(source string) (map[string]*compiler.Contract, error) {
-	solc, err := s.getSolc()
-	if err != nil {
-		return nil, err
-	}
-
-	if solc == nil {
-		return nil, errors.New("solc (solidity compiler) not found")
-	}
-
-	return solc.Compile(source)
-}
-
 // ProtocolVersion returns the current Ethereum protocol version this node supports
 func (s *PublicEthereumAPI) ProtocolVersion() *rpc.HexNumber {
 	return rpc.NewHexNumber(s.b.ProtocolVersion())
@@ -1416,31 +1379,6 @@ func (s *PublicTransactionPoolAPI) Resend(ctx context.Context, tx *Tx, gasPrice,
 	return common.Hash{}, fmt.Errorf("Transaction %#x not found", tx.Hash)
 }
 
-// PrivateAdminAPI is the collection of Etheruem APIs exposed over the private
-// admin endpoint.
-type PrivateAdminAPI struct {
-	b        Backend
-	solcPath *string
-	solc     **compiler.Solidity
-}
-
-// NewPrivateAdminAPI creates a new API definition for the private admin methods
-// of the Ethereum service.
-func NewPrivateAdminAPI(b Backend, solcPath *string, solc **compiler.Solidity) *PrivateAdminAPI {
-	return &PrivateAdminAPI{b, solcPath, solc}
-}
-
-// SetSolc sets the Solidity compiler path to be used by the node.
-func (api *PrivateAdminAPI) SetSolc(path string) (string, error) {
-	var err error
-	*api.solcPath = path
-	*api.solc, err = compiler.New(path)
-	if err != nil {
-		return "", err
-	}
-	return (*api.solc).Info(), nil
-}
-
 // PublicDebugAPI is the collection of Etheruem APIs exposed over the public
 // debugging endpoint.
 type PublicDebugAPI struct {
diff --git a/internal/ethapi/backend.go b/internal/ethapi/backend.go
index d112a6aef..791a06925 100644
--- a/internal/ethapi/backend.go
+++ b/internal/ethapi/backend.go
@@ -22,7 +22,6 @@ import (
 
 	"github.com/ethereum/go-ethereum/accounts"
 	"github.com/ethereum/go-ethereum/common"
-	"github.com/ethereum/go-ethereum/common/compiler"
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/core/vm"
@@ -69,12 +68,13 @@ type State interface {
 	GetNonce(ctx context.Context, addr common.Address) (uint64, error)
 }
 
-func GetAPIs(apiBackend Backend, solcPath *string, solc **compiler.Solidity) []rpc.API {
-	return []rpc.API{
+func GetAPIs(apiBackend Backend, solcPath string) []rpc.API {
+	compiler := makeCompilerAPIs(solcPath)
+	all := []rpc.API{
 		{
 			Namespace: "eth",
 			Version:   "1.0",
-			Service:   NewPublicEthereumAPI(apiBackend, solcPath, solc),
+			Service:   NewPublicEthereumAPI(apiBackend),
 			Public:    true,
 		}, {
 			Namespace: "eth",
@@ -92,10 +92,6 @@ func GetAPIs(apiBackend Backend, solcPath *string, solc **compiler.Solidity) []r
 			Service:   NewPublicTxPoolAPI(apiBackend),
 			Public:    true,
 		}, {
-			Namespace: "admin",
-			Version:   "1.0",
-			Service:   NewPrivateAdminAPI(apiBackend, solcPath, solc),
-		}, {
 			Namespace: "debug",
 			Version:   "1.0",
 			Service:   NewPublicDebugAPI(apiBackend),
@@ -116,4 +112,5 @@ func GetAPIs(apiBackend Backend, solcPath *string, solc **compiler.Solidity) []r
 			Public:    false,
 		},
 	}
+	return append(compiler, all...)
 }
diff --git a/internal/ethapi/solc.go b/internal/ethapi/solc.go
new file mode 100644
index 000000000..b9acc518b
--- /dev/null
+++ b/internal/ethapi/solc.go
@@ -0,0 +1,82 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package ethapi
+
+import (
+	"sync"
+
+	"github.com/ethereum/go-ethereum/common/compiler"
+	"github.com/ethereum/go-ethereum/rpc"
+)
+
+func makeCompilerAPIs(solcPath string) []rpc.API {
+	c := &compilerAPI{solc: solcPath}
+	return []rpc.API{
+		{
+			Namespace: "eth",
+			Version:   "1.0",
+			Service:   (*PublicCompilerAPI)(c),
+			Public:    true,
+		},
+		{
+			Namespace: "admin",
+			Version:   "1.0",
+			Service:   (*CompilerAdminAPI)(c),
+			Public:    true,
+		},
+	}
+}
+
+type compilerAPI struct {
+	// This lock guards the solc path set through the API.
+	// It also ensures that only one solc process is used at
+	// any time.
+	mu   sync.Mutex
+	solc string
+}
+
+type CompilerAdminAPI compilerAPI
+
+// SetSolc sets the Solidity compiler path to be used by the node.
+func (api *CompilerAdminAPI) SetSolc(path string) (string, error) {
+	api.mu.Lock()
+	defer api.mu.Unlock()
+	info, err := compiler.SolidityVersion(path)
+	if err != nil {
+		return "", err
+	}
+	api.solc = path
+	return info.FullVersion, nil
+}
+
+type PublicCompilerAPI compilerAPI
+
+// CompileSolidity compiles the given solidity source.
+func (api *PublicCompilerAPI) CompileSolidity(source string) (map[string]*compiler.Contract, error) {
+	api.mu.Lock()
+	defer api.mu.Unlock()
+	return compiler.CompileSolidityString(api.solc, source)
+}
+
+func (api *PublicCompilerAPI) GetCompilers() ([]string, error) {
+	api.mu.Lock()
+	defer api.mu.Unlock()
+	if _, err := compiler.SolidityVersion(api.solc); err == nil {
+		return []string{"Solidity"}, nil
+	}
+	return []string{}, nil
+}