Add lookup abstraction for locating executable files

Signed-off-by: Evan Lezar <elezar@nvidia.com>

internal/lookup/file.go

@@ -0,0 +1,85 @@
+/*
+# Copyright (c) 2021, NVIDIA CORPORATION.  All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+*/
+
+package lookup
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	log "github.com/sirupsen/logrus"
+)
+
+// file can be used to locate file (or file-like elements) at a specified set of
+// prefixes. The validity of a file is determined by a filter function.
+type file struct {
+	logger   *log.Logger
+	prefixes []string
+	filter   func(string) error
+}
+
+// NewFileLocator creates a Locator that can be used to find files at the specified root. A logger
+// can also be specified.
+func NewFileLocator(logger *log.Logger, root string) Locator {
+	l := newFileLocator(logger, root)
+
+	return &l
+}
+
+func newFileLocator(logger *log.Logger, root string) file {
+	return file{
+		logger:   logger,
+		prefixes: []string{root},
+		filter:   assertFile,
+	}
+}
+
+var _ Locator = (*file)(nil)
+
+// Locate attempts to find the specified file. All prefixes are searched and any matching
+// candidates are returned. If no matches are found, an error is returned.
+func (p file) Locate(filename string) ([]string, error) {
+	var filenames []string
+	for _, prefix := range p.prefixes {
+		candidate := filepath.Join(prefix, filename)
+		p.logger.Debugf("Checking candidate '%v'", candidate)
+		err := p.filter(candidate)
+		if err != nil {
+			p.logger.Debugf("Candidate '%v' does not meet requirements: %v", candidate, err)
+			continue
+		}
+		filenames = append(filenames, candidate)
+	}
+	if len(filename) == 0 {
+		return nil, fmt.Errorf("file %v not found", filename)
+	}
+	return filenames, nil
+}
+
+// assertFile checks whether the specified path is a regular file
+func assertFile(filename string) error {
+	info, err := os.Stat(filename)
+	if err != nil {
+		return fmt.Errorf("error getting info for %v: %v", filename, err)
+	}
+
+	if info.IsDir() {
+		return fmt.Errorf("specified path '%v' is a directory", filename)
+	}
+
+	return nil
+}

internal/lookup/locator.go

@@ -0,0 +1,24 @@
+/*
+# Copyright (c) 2021, NVIDIA CORPORATION.  All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+*/
+
+package lookup
+
+//go:generate moq -stub -out locator_mock.go . Locator
+
+// Locator defines the interface for locating files on a system.
+type Locator interface {
+	Locate(string) ([]string, error)
+}

internal/lookup/locator_mock.go

@@ -0,0 +1,77 @@
+// Code generated by moq; DO NOT EDIT.
+// github.com/matryer/moq
+
+package lookup
+
+import (
+	"sync"
+)
+
+// Ensure, that LocatorMock does implement Locator.
+// If this is not the case, regenerate this file with moq.
+var _ Locator = &LocatorMock{}
+
+// LocatorMock is a mock implementation of Locator.
+//
+// 	func TestSomethingThatUsesLocator(t *testing.T) {
+//
+// 		// make and configure a mocked Locator
+// 		mockedLocator := &LocatorMock{
+// 			LocateFunc: func(s string) ([]string, error) {
+// 				panic("mock out the Locate method")
+// 			},
+// 		}
+//
+// 		// use mockedLocator in code that requires Locator
+// 		// and then make assertions.
+//
+// 	}
+type LocatorMock struct {
+	// LocateFunc mocks the Locate method.
+	LocateFunc func(s string) ([]string, error)
+
+	// calls tracks calls to the methods.
+	calls struct {
+		// Locate holds details about calls to the Locate method.
+		Locate []struct {
+			// S is the s argument value.
+			S string
+		}
+	}
+	lockLocate sync.RWMutex
+}
+
+// Locate calls LocateFunc.
+func (mock *LocatorMock) Locate(s string) ([]string, error) {
+	callInfo := struct {
+		S string
+	}{
+		S: s,
+	}
+	mock.lockLocate.Lock()
+	mock.calls.Locate = append(mock.calls.Locate, callInfo)
+	mock.lockLocate.Unlock()
+	if mock.LocateFunc == nil {
+		var (
+			stringsOut []string
+			errOut     error
+		)
+		return stringsOut, errOut
+	}
+	return mock.LocateFunc(s)
+}
+
+// LocateCalls gets all the calls that were made to Locate.
+// Check the length with:
+//     len(mockedLocator.LocateCalls())
+func (mock *LocatorMock) LocateCalls() []struct {
+	S string
+} {
+	var calls []struct {
+		S string
+	}
+	mock.lockLocate.RLock()
+	calls = mock.calls.Locate
+	mock.lockLocate.RUnlock()
+	return calls
+}

internal/lookup/path.go

@@ -0,0 +1,93 @@
+/*
+# Copyright (c) 2021, NVIDIA CORPORATION.  All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+*/
+
+package lookup
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	log "github.com/sirupsen/logrus"
+)
+
+const (
+	envPath = "PATH"
+)
+
+var defaultPaths = []string{"/usr/local/sbin", "/usr/local/bin", "/usr/sbin", "/usr/bin", "/sbin", "/bin"}
+
+type path struct {
+	file
+}
+
+// NewPathLocator creates a locator to fine executable files in the path. A logger can also be specified.
+func NewPathLocator(logger *log.Logger, root string) Locator {
+	pathEnv := os.Getenv(envPath)
+	paths := filepath.SplitList(pathEnv)
+
+	if root != "" {
+		paths = append(paths, defaultPaths...)
+	}
+
+	var prefixes []string
+	for _, dir := range paths {
+		prefixes = append(prefixes, filepath.Join(root, dir))
+	}
+	l := path{
+		file: file{
+			logger:   logger,
+			prefixes: prefixes,
+			filter:   assertExecutable,
+		},
+	}
+	return &l
+}
+
+var _ Locator = (*path)(nil)
+
+// Locate finds executable files in the path. If a relative or absolute path is specified, the prefix paths are not considered.
+func (p path) Locate(filename string) ([]string, error) {
+	// For absolute paths we ensure that it is executable
+	if strings.Contains(filename, "/") {
+		err := assertExecutable(filename)
+		if err != nil {
+			return nil, fmt.Errorf("absolute path %v is not an executable file: %v", filename, err)
+		}
+		return []string{filename}, nil
+	}
+
+	return p.file.Locate(filename)
+}
+
+// assertExecutable checks whether the specified path is an execuable file.
+func assertExecutable(filename string) error {
+	err := assertFile(filename)
+	if err != nil {
+		return err
+	}
+	info, err := os.Stat(filename)
+	if err != nil {
+		return err
+	}
+
+	if info.Mode()&0111 == 0 {
+		return fmt.Errorf("specified file '%v' is not executable", filename)
+	}
+
+	return nil
+}