replicate.go

Documentation: github.com/bazelbuild/rules_go/go/tools/builders

     1  // Copyright 2018 The Bazel Authors. All rights reserved.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //    http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // stdlib builds the standard library in the appropriate mode into a new goroot.
    16  package main
    17  
    18  import (
    19  	"fmt"
    20  	"io"
    21  	"os"
    22  	"path/filepath"
    23  )
    24  
    25  type replicateMode int
    26  
    27  const (
    28  	copyMode replicateMode = iota
    29  	hardlinkMode
    30  	softlinkMode
    31  )
    32  
    33  type replicateOption func(*replicateConfig)
    34  type replicateConfig struct {
    35  	removeFirst bool
    36  	fileMode    replicateMode
    37  	dirMode     replicateMode
    38  	paths       []string
    39  }
    40  
    41  func replicatePaths(paths ...string) replicateOption {
    42  	return func(config *replicateConfig) {
    43  		config.paths = append(config.paths, paths...)
    44  	}
    45  }
    46  
    47  // replicatePrepare is the common preparation steps for a replication entry
    48  func replicatePrepare(dst string, config *replicateConfig) error {
    49  	dir := filepath.Dir(dst)
    50  	if err := os.MkdirAll(dir, 0755); err != nil {
    51  		return fmt.Errorf("Failed to make %s: %v", dir, err)
    52  	}
    53  	if config.removeFirst {
    54  		_ = os.Remove(dst)
    55  	}
    56  	return nil
    57  }
    58  
    59  // replicateFile is called internally by replicate to map a single file from src into dst.
    60  func replicateFile(src, dst string, config *replicateConfig) error {
    61  	if err := replicatePrepare(dst, config); err != nil {
    62  		return err
    63  	}
    64  	switch config.fileMode {
    65  	case copyMode:
    66  		in, err := os.Open(src)
    67  		if err != nil {
    68  			return err
    69  		}
    70  		defer in.Close()
    71  		out, err := os.Create(dst)
    72  		if err != nil {
    73  			return err
    74  		}
    75  		_, err = io.Copy(out, in)
    76  		closeerr := out.Close()
    77  		if err != nil {
    78  			return err
    79  		}
    80  		if closeerr != nil {
    81  			return closeerr
    82  		}
    83  		s, err := os.Stat(src)
    84  		if err != nil {
    85  			return err
    86  		}
    87  		if err := os.Chmod(dst, s.Mode()); err != nil {
    88  			return err
    89  		}
    90  		return nil
    91  	case hardlinkMode:
    92  		return os.Link(src, dst)
    93  	case softlinkMode:
    94  		return os.Symlink(src, dst)
    95  	default:
    96  		return fmt.Errorf("Invalid replication mode %d", config.fileMode)
    97  	}
    98  }
    99  
   100  // replicateDir makes a tree of files visible in a new location.
   101  // It is allowed to take any efficient method of doing so.
   102  func replicateDir(src, dst string, config *replicateConfig) error {
   103  	if err := replicatePrepare(dst, config); err != nil {
   104  		return err
   105  	}
   106  	switch config.dirMode {
   107  	case copyMode:
   108  		return filepath.Walk(src, func(path string, f os.FileInfo, err error) error {
   109  			if f.IsDir() {
   110  				return nil
   111  			}
   112  			relative, err := filepath.Rel(src, path)
   113  			if err != nil {
   114  				return err
   115  			}
   116  			return replicateFile(path, filepath.Join(dst, relative), config)
   117  		})
   118  	case hardlinkMode:
   119  		return os.Link(src, dst)
   120  	case softlinkMode:
   121  		return os.Symlink(src, dst)
   122  	default:
   123  		return fmt.Errorf("Invalid replication mode %d", config.fileMode)
   124  	}
   125  }
   126  
   127  // replicateTree is called for each single src dst pair.
   128  func replicateTree(src, dst string, config *replicateConfig) error {
   129  	if err := os.RemoveAll(dst); err != nil {
   130  		return fmt.Errorf("Failed to remove file at destination %s: %v", dst, err)
   131  	}
   132  	if l, err := filepath.EvalSymlinks(src); err != nil {
   133  		return err
   134  	} else {
   135  		src = l
   136  	}
   137  	if s, err := os.Stat(src); err != nil {
   138  		return err
   139  	} else if s.IsDir() {
   140  		return replicateDir(src, dst, config)
   141  	}
   142  	return replicateFile(src, dst, config)
   143  }
   144  
   145  // replicate makes a tree of files visible in a new location.
   146  // You control how it does so using options, by default it presumes the entire tree
   147  // of files rooted at src must be visible at dst, and that it should do so by copying.
   148  // src is allowed to be a file, in which case just the one file is copied.
   149  func replicate(src, dst string, options ...replicateOption) error {
   150  	config := replicateConfig{
   151  		removeFirst: true,
   152  	}
   153  	for _, option := range options {
   154  		option(&config)
   155  	}
   156  	if len(config.paths) == 0 {
   157  		return replicateTree(src, dst, &config)
   158  	}
   159  	for _, base := range config.paths {
   160  		from := filepath.Join(src, base)
   161  		to := filepath.Join(dst, base)
   162  		if err := replicateTree(from, to, &config); err != nil {
   163  			return err
   164  		}
   165  	}
   166  	return nil
   167  }
   168
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