如何处理使用承诺递归读取目录树
how to handle reading a directory tree recursively using promises
我正在尝试编写一个函数来完成与以下使用带有承诺模式的回调模式编写的函数相同的功能:
function readdirRecursive(path,handler,callback) {
var errs = [],
tree = {};
fs.readdir(path,function(err,dir) {
if(err)return callback(err);
var pending = dir.length;
if(!pending)return callback(null,tree);
dir.forEach(function(file) {
var newPath = Path.join(path,file);
fs.stat(newPath,function(err,stats) {
if(stats.isDirectory()) {
readdirRecursive(newPath,handler,function(err,subtree) {
tree[file] = subtree
handler(tree,newPath,file,"directory",function(err) {
if(err)errs.push(err);
if(!--pending)return callback(errs.length>0?errs:null,tree);
});
});
} else {
tree[file] = null;
handler(tree,newPath,file,"file",function(err) {
if(err)errs.push(err);
if(!--pending)return callback(errs.length>0?errs:null,tree);
});
}
});
});
});
};
这是我目前的尝试:
function readdirRecursive(path) {
var tree = {};
return Q.Promise(function(resolve,reject,notify) {
return readdir(path)
.then(function(dir) {
var futures = [];
var pending = dir.length;
if(!pending)return resolve(tree);
dir.forEach(function(file) {
var deferred = Q.defer();
var subPath = Path.join(path,file);
futures.push(stat(subPath)
.then(function(stats) {
if(stats.isDirectory()) {
tree[file] = tree;
var sub = readdirRecursive(subPath)
sub
.then(function(subtree) {
notify({
path:subPath,
name:file,
type:"directory",
done:deferred,
pending:pending
});
//return subtree;
},reject,notify);
} else {
tree[file] = null;
notify({
tree:tree,
path:subPath,
name:file,
type:"file",
done:deferred,
pending:pending
});
//return null;
}
//console.log("tree",tree);
deferred.promise()
.then(function() {
console.log("pending promise");
if(!--pending)resolve(tree);
}
,function(err) {
reject();
});
}));
});
return Q.all(futures)
.then(function(futures) {
console.log("hi",futures);
});
});
});
};
此代码将遍历整个树,但不会 return 树,并且会发生通知操作,但延迟承诺永远不会解决。
当延迟承诺在通知事件之前启动时,什么也不会发生。
我知道我可以通过将完成的函数传递给进度事件来解决这个问题,而不是尝试给出某种承诺,但我想在这里尽可能充分地利用承诺,例如,这段代码完全符合我的要求:
function readdirRecursive(path) {
var tree = {};
return Q.Promise(function(resolve,reject,notify) {
return readdir(path)
.then(function(dir) {
var futures = [];
var pending = dir.length;
if(!pending)return resolve(tree);
dir.forEach(function(file) {
var deferred = Q.defer();
var subPath = Path.join(path,file);
console.log("file",file);
/*deferred.promise()
.then(function() {
console.log("pending promise");
if(!--pending)resolve(tree);
}
,function(err) {
reject();
});*/
futures.push(stat(subPath)
.then(function(stats) {
if(stats.isDirectory()) {
var sub = readdirRecursive(subPath)
sub
.then(function(subtree) {
tree[file] = subtree
notify({
path:subPath,
name:file,
type:"directory",
done:function(err) {
console.log("pending promise");
if(err)return reject(err);
if(!--pending)resolve(tree);
},
pending:pending
});
//return subtree;
},reject,notify);
} else {
tree[file] = null;
notify({
tree:tree,
path:subPath,
name:file,
type:"file",
done:function(err) {
console.log("pending promise");
if(err)return reject();
if(!--pending)resolve(tree);
},
pending:pending
});
//return null;
}
//console.log("tree",tree);
}));
});
return Q.all(futures)
.then(function(futures) {
console.log("hi",futures);
});
});
});
};
这是将执行这些功能的代码:
readdirRecursive("../").then(function(tree) {
console.log("TREE!!!",tree);
},function(err) {
console.log("ERROR",err);
},function(progress) {
console.log("PRGRESS WAS MADE",progress);
progress.done();
});
我的第一个想法是简单地将您的原始功能包装在一个承诺中。这通常是我在没有 re-engineering 底层代码的情况下执行此操作的方式:
function readdirRecursiveWithPromise (path, handler) {
return new Promise((resolve, reject) => {
readdirRecursive(path, handler, (err, tree) => {
if (err) {
reject(err);
}
else {
resolve(tree);
}
});
})
}
不幸的是,当我尝试测试此代码时,我发现了您的代码的几个潜在问题。
首先,我不知道你的 'handler' 应该做什么。您没有对此提供解释或描述它应该做什么。这对问题来说很重要,因为它控制着最终回调是否最终被调用,所以我可以推测 'handler' 控制着这个操作,如果你的 'callback' 没有被调用,它可能是由于您 'handler'.
中的逻辑
下一个问题是您的 'pending' 变量设置为 和 目录的文件总数,但它只针对目录递减。因此,您的 'pending' 变量永远不会达到 0,并且永远不会调用调用回调的条件代码。
所以我要摆脱 'handler' 和 'pending',我将向您展示我如何用 promises 从头开始重写它。
这是完整的工作代码示例:https://github.com/ashleydavis/read-directory-with-promises。请继续阅读以获取解释。
让我们从 非 递归的 promise-based 版本的 readdir 开始:
function readdir (path) { // Promise-based version of readdir.
return new Promise((resolve, reject) => { // Wrap the underlying operation in a promise.
fs.readdir(path, (err, files) => {
if (err) {
reject(err); // On error, reject the promise.
}
else {
resolve(files); // On success, resolve the promise.
}
});
});
};
我们还需要一个 promise-based 函数来确定特定路径的类型(文件或目录):
function determineType (parentPath, childPath) { // Promise-based function to determine if the path is a file or directory.
return new Promise((resolve, reject) => {
fs.stat(path.join(parentPath, childPath), (err, stats) => {
if (err) {
reject(err);
}
else {
resolve({
path: childPath,
type: stats.isDirectory() ? 'directory' : 'file' // Check if it's a directory or a file.
});
}
});
});
};
现在我们可以扩展 determineType
并创建一个函数,它接受一组路径并确定每个路径的类型。这使用 Promise.all
并行执行多个异步操作:
function determineTypes (parentPath, paths) { // Async function to determine if child paths are directories or files.
return Promise.all(
paths.map(
childPath => determineType(parentPath, childPath) // Is the path a directory or a file?
)
);
};
现在我们可以构建 readdir
的 promise-based 递归版本:
function readdirTree (rootPath) { // Read an entire directory tree, the promise-based recursive version.
return readdir(rootPath) // Initial non-recursive directory read.
.then(childPaths => determineTypes(rootPath, childPaths)) // Figure out the type of child paths.
.then(children => {
return Promise.all(children // Use Promise.all to figure out all sub-trees in a parallel.
.filter(child => child.type === 'directory') // Filter so we only directories are remaining.
.map(child => {
return readdirTree(path.join(rootPath, child.path)) // It's a directory, recurse to the next level down.
.then(subTree => {
return {
path: child.path,
subTree: subTree,
};
});
})
);
})
.then(children => {
const tree = {}; // Reorganise the list of directories into a tree.
children.forEach(directory => {
tree[directory.path] = directory.subTree;
});
return tree;
});
};
这是一个使用示例:
readdirTree("c:\some-directory")
.then(tree => {
console.log("tree:");
console.log(tree);
})
.catch(err => {
console.error("error:");
console.error(err);
});
我在 Github 中为您提供了一个完整的示例:https://github.com/ashleydavis/read-directory-with-promises
希望它能帮助你前进。
我正在尝试编写一个函数来完成与以下使用带有承诺模式的回调模式编写的函数相同的功能:
function readdirRecursive(path,handler,callback) {
var errs = [],
tree = {};
fs.readdir(path,function(err,dir) {
if(err)return callback(err);
var pending = dir.length;
if(!pending)return callback(null,tree);
dir.forEach(function(file) {
var newPath = Path.join(path,file);
fs.stat(newPath,function(err,stats) {
if(stats.isDirectory()) {
readdirRecursive(newPath,handler,function(err,subtree) {
tree[file] = subtree
handler(tree,newPath,file,"directory",function(err) {
if(err)errs.push(err);
if(!--pending)return callback(errs.length>0?errs:null,tree);
});
});
} else {
tree[file] = null;
handler(tree,newPath,file,"file",function(err) {
if(err)errs.push(err);
if(!--pending)return callback(errs.length>0?errs:null,tree);
});
}
});
});
});
};
这是我目前的尝试:
function readdirRecursive(path) {
var tree = {};
return Q.Promise(function(resolve,reject,notify) {
return readdir(path)
.then(function(dir) {
var futures = [];
var pending = dir.length;
if(!pending)return resolve(tree);
dir.forEach(function(file) {
var deferred = Q.defer();
var subPath = Path.join(path,file);
futures.push(stat(subPath)
.then(function(stats) {
if(stats.isDirectory()) {
tree[file] = tree;
var sub = readdirRecursive(subPath)
sub
.then(function(subtree) {
notify({
path:subPath,
name:file,
type:"directory",
done:deferred,
pending:pending
});
//return subtree;
},reject,notify);
} else {
tree[file] = null;
notify({
tree:tree,
path:subPath,
name:file,
type:"file",
done:deferred,
pending:pending
});
//return null;
}
//console.log("tree",tree);
deferred.promise()
.then(function() {
console.log("pending promise");
if(!--pending)resolve(tree);
}
,function(err) {
reject();
});
}));
});
return Q.all(futures)
.then(function(futures) {
console.log("hi",futures);
});
});
});
};
此代码将遍历整个树,但不会 return 树,并且会发生通知操作,但延迟承诺永远不会解决。
当延迟承诺在通知事件之前启动时,什么也不会发生。
我知道我可以通过将完成的函数传递给进度事件来解决这个问题,而不是尝试给出某种承诺,但我想在这里尽可能充分地利用承诺,例如,这段代码完全符合我的要求:
function readdirRecursive(path) {
var tree = {};
return Q.Promise(function(resolve,reject,notify) {
return readdir(path)
.then(function(dir) {
var futures = [];
var pending = dir.length;
if(!pending)return resolve(tree);
dir.forEach(function(file) {
var deferred = Q.defer();
var subPath = Path.join(path,file);
console.log("file",file);
/*deferred.promise()
.then(function() {
console.log("pending promise");
if(!--pending)resolve(tree);
}
,function(err) {
reject();
});*/
futures.push(stat(subPath)
.then(function(stats) {
if(stats.isDirectory()) {
var sub = readdirRecursive(subPath)
sub
.then(function(subtree) {
tree[file] = subtree
notify({
path:subPath,
name:file,
type:"directory",
done:function(err) {
console.log("pending promise");
if(err)return reject(err);
if(!--pending)resolve(tree);
},
pending:pending
});
//return subtree;
},reject,notify);
} else {
tree[file] = null;
notify({
tree:tree,
path:subPath,
name:file,
type:"file",
done:function(err) {
console.log("pending promise");
if(err)return reject();
if(!--pending)resolve(tree);
},
pending:pending
});
//return null;
}
//console.log("tree",tree);
}));
});
return Q.all(futures)
.then(function(futures) {
console.log("hi",futures);
});
});
});
};
这是将执行这些功能的代码:
readdirRecursive("../").then(function(tree) {
console.log("TREE!!!",tree);
},function(err) {
console.log("ERROR",err);
},function(progress) {
console.log("PRGRESS WAS MADE",progress);
progress.done();
});
我的第一个想法是简单地将您的原始功能包装在一个承诺中。这通常是我在没有 re-engineering 底层代码的情况下执行此操作的方式:
function readdirRecursiveWithPromise (path, handler) {
return new Promise((resolve, reject) => {
readdirRecursive(path, handler, (err, tree) => {
if (err) {
reject(err);
}
else {
resolve(tree);
}
});
})
}
不幸的是,当我尝试测试此代码时,我发现了您的代码的几个潜在问题。
首先,我不知道你的 'handler' 应该做什么。您没有对此提供解释或描述它应该做什么。这对问题来说很重要,因为它控制着最终回调是否最终被调用,所以我可以推测 'handler' 控制着这个操作,如果你的 'callback' 没有被调用,它可能是由于您 'handler'.
中的逻辑下一个问题是您的 'pending' 变量设置为 和 目录的文件总数,但它只针对目录递减。因此,您的 'pending' 变量永远不会达到 0,并且永远不会调用调用回调的条件代码。
所以我要摆脱 'handler' 和 'pending',我将向您展示我如何用 promises 从头开始重写它。
这是完整的工作代码示例:https://github.com/ashleydavis/read-directory-with-promises。请继续阅读以获取解释。
让我们从 非 递归的 promise-based 版本的 readdir 开始:
function readdir (path) { // Promise-based version of readdir.
return new Promise((resolve, reject) => { // Wrap the underlying operation in a promise.
fs.readdir(path, (err, files) => {
if (err) {
reject(err); // On error, reject the promise.
}
else {
resolve(files); // On success, resolve the promise.
}
});
});
};
我们还需要一个 promise-based 函数来确定特定路径的类型(文件或目录):
function determineType (parentPath, childPath) { // Promise-based function to determine if the path is a file or directory.
return new Promise((resolve, reject) => {
fs.stat(path.join(parentPath, childPath), (err, stats) => {
if (err) {
reject(err);
}
else {
resolve({
path: childPath,
type: stats.isDirectory() ? 'directory' : 'file' // Check if it's a directory or a file.
});
}
});
});
};
现在我们可以扩展 determineType
并创建一个函数,它接受一组路径并确定每个路径的类型。这使用 Promise.all
并行执行多个异步操作:
function determineTypes (parentPath, paths) { // Async function to determine if child paths are directories or files.
return Promise.all(
paths.map(
childPath => determineType(parentPath, childPath) // Is the path a directory or a file?
)
);
};
现在我们可以构建 readdir
的 promise-based 递归版本:
function readdirTree (rootPath) { // Read an entire directory tree, the promise-based recursive version.
return readdir(rootPath) // Initial non-recursive directory read.
.then(childPaths => determineTypes(rootPath, childPaths)) // Figure out the type of child paths.
.then(children => {
return Promise.all(children // Use Promise.all to figure out all sub-trees in a parallel.
.filter(child => child.type === 'directory') // Filter so we only directories are remaining.
.map(child => {
return readdirTree(path.join(rootPath, child.path)) // It's a directory, recurse to the next level down.
.then(subTree => {
return {
path: child.path,
subTree: subTree,
};
});
})
);
})
.then(children => {
const tree = {}; // Reorganise the list of directories into a tree.
children.forEach(directory => {
tree[directory.path] = directory.subTree;
});
return tree;
});
};
这是一个使用示例:
readdirTree("c:\some-directory")
.then(tree => {
console.log("tree:");
console.log(tree);
})
.catch(err => {
console.error("error:");
console.error(err);
});
我在 Github 中为您提供了一个完整的示例:https://github.com/ashleydavis/read-directory-with-promises
希望它能帮助你前进。