git ssb

1
const Graph = require('ipld-graph-builder')
2
const Buffer = require('safe-buffer').Buffer
3
const Uint1Array = require('uint1array')
4
const TextEncoder = require('text-encoding').TextEncoder
5
6
const encoder = new TextEncoder('utf-8')
7
8
const RadixTree = module.exports = class RadixTree {
9
  /**
10
   * @param opts
11
   * @param opts.root {object} a merkle root to a radix tree. If none, RadixTree will create an new root.
12
   * @param opts.graph {object} an instance of [ipld-graph-builder](https://github.com/ipld/js-ipld-graph-builder) alternitvly `opts.dag` can be used
13
   * @param opts.dag {object} an instance if [ipfs.dag](https://github.com/ipfs/js-ipfs#dag). If there is no `opts.graph` this will be used to create a new graph instance.
14
   */
15
  constructor (opts) {
16
    this.root = opts.root || {'/': RadixTree.emptyTreeState}
17
    this.graph = opts.graph || new Graph(opts.dag)
18
  }
19
20
  /**
21
   * returns the state of an empty tree
22
   */
23
  static get emptyTreeState () {
24
    return [undefined, undefined]
25
  }
26
27
  /**
28
   * returns an Uint1Array constructir which is used to repersent keys
29
   * @returns {object}
30
   */
31
  static get ArrayConstructor () {
32
    return Uint1Array
33
  }
34
35
  /**
36
   * converts a TypedArray or Buffer to an Uint1Array
37
   * @param {TypedArray} array - the array to convert
38
   * @returns {TypedArray}
39
   */
40
  static toTypedArray (array) {
41
    return new RadixTree.ArrayConstructor(new Uint8Array(array).buffer)
42
  }
43
44
  async _get (key) {
45
    let index = 0
46
    let root = this.root
47
    let parent
48
49
    while (1) {
50
      // load the root
51
      const exNode = await this.graph.get(root, EXTENSION, true)
52
      if (exNode) {
53
        let extensionIndex = 0
54
        const extension = getExtension(root)
55
        const extensionLen = extension.length
56
        let subKey
57
        subKey = key.slice(index, index + extensionLen)
58
59
        // checks the extension against the key
60
        while (extensionIndex < extensionLen && extension[extensionIndex] === subKey[extensionIndex]) {
61
          extensionIndex++
62
        }
63
        index += extensionIndex
64
        // check if we compelete travered the extension
65
        if (extensionIndex !== extensionLen) {
66
          return {
67
            extensionIndex: extensionIndex,
68
            root: root,
69
            index: index
70
          }
71
        }
72
      }
73
74
      let keySegment = key[index]
75
      if (keySegment !== undefined) {
76
        const branch = getBranch(root)
77
        await this.graph.get(branch, keySegment, true)
78
        // preseves the '/'
79
        const nextRoot = branch[keySegment]
80
        if (!nextRoot) {
81
          return {
82
            root: root,
83
            index: index
84
          }
85
        } else {
86
          parent = root
87
          root = nextRoot
88
        }
89
      } else {
90
        break
91
      }
92
93
      index++
94
    }
95
96
    let value = getValue(root)
97
98
    if (value && value['/']) {
99
      value = await this.graph.get(root, VALUE, true)
100
    }
101
102
    return {
103
      value: value,
104
      root: root,
105
      parent: parent,
106
      index: index
107
    }
108
  }
109
110
  /**
111
   * gets a value given a key
112
   * @param {*} key
113
   * @return {Promise}
114
   */
115
  async get (key) {
116
    key = RadixTree.formatKey(key)
117
    const result = await this._get(key)
118
    return result.value
119
  }
120
121
  /**
122
   * stores a value at a given key
123
   * @param {*} key
124
   * @return {Promise}
125
   */
126
  async set (key, value) {
127
    key = RadixTree.formatKey(key)
128
129
    if (value.length > 32) {
130
      value = {'/': value}
131
    }
132
133
    const result = await this._get(key)
134
    let root = result.root
135
136
    if (result.value) {
137
      setValue(root, value)
138
    } else {
139
      if (result.extensionIndex !== undefined) {
140
        // split the extension node in two
141
        let extension = getExtension(root)
142
        const extensionKey = extension[result.extensionIndex]
143
        const remExtension = extension.subarray(result.extensionIndex + 1)
144
        extension = extension.subarray(0, result.extensionIndex)
145
146
        setExtension(root, remExtension)
147
        const branch = []
148
        branch[extensionKey] = {'/': root['/']}
149
        root['/'] = createNode(extension, branch)['/']
150
      }
151
152
      // if there are remaning key segments create an extension node
153
      if (result.index < key.length) {
154
        const keySegment = key[result.index]
155
        const extension = key.subarray(result.index + 1, key.length)
156
        const newNode = createNode(extension, [], value)
157
        const rootBranch = getBranch(root)
158
        rootBranch[keySegment] = newNode
159
        setBranch(root, rootBranch)
160
      } else {
161
        setValue(root, value)
162
      }
163
    }
164
  }
165
166
  /**
167
   * deletes a value at a given key
168
   * @param {*} key
169
   * @return {Promise}
170
   */
171
  async delete (key) {
172
    key = RadixTree.formatKey(key)
173
    const results = await this._get(key)
174
    if (results.value !== undefined) {
175
      const root = results.root
176
      const parent = results.parent
177
178
      deleteValue(root)
179
180
      const branch = getBranch(root)
181
      if (branch.some(el => el !== undefined)) {
182
        joinNodes(root)
183
      } else {
184
        if (!parent) {
185
          root['/'] = RadixTree.emptyTreeState
186
        } else {
187
          let branch = getBranch(parent)
188
          branch = branch.map(node => node === root ? undefined : node)
189
          setBranch(parent, branch)
190
191
          joinNodes(parent)
192
        }
193
      }
194
    }
195
196
    function joinNodes (root) {
197
      if (getValue(root) === undefined) {
198
        let index
199
        const branch = getBranch(root)
200
        const nodes = branch.filter((node, i) => {
201
          if (node) {
202
            index = i
203
            return true
204
          }
205
        })
206
207
        if (nodes.length === 1) {
208
          const child = nodes[0]
209
          const pExtension = getExtension(root)
210
          const childExtension = getExtension(child)
211
          const newExtension = new RadixTree.ArrayConstructor(pExtension.length + childExtension.length + 1)
212
213
          newExtension.set(pExtension)
214
          newExtension[pExtension.length] = index
215
          newExtension.set(childExtension, pExtension.length + 1)
216
217
          setExtension(child, newExtension)
218
          root['/'] = child['/']
219
        }
220
      }
221
    }
222
  }
223
224
  /**
225
   * creates a merkle root for the current tree and stores the data perstantly
226
   * @returns {Promise}
227
   */
228
  flush () {
229
    return this.graph.flush(this.root)
230
  }
231
232
  static formatKey (key) {
233
    if (typeof key === 'string') {
234
      key = encoder.encode(key)
235
    }
236
237
    if (key.constructor !== RadixTree.ArrayConstructor) {
238
      return new RadixTree.ArrayConstructor(key.buffer)
239
    } else {
240
      return key
241
    }
242
  }
243
}
244
245
function createNode (ex, branch, value) {
246
  const node = {
247
    '/': []
248
  }
249
250
  setValue(node, value)
251
  setExtension(node, ex)
252
  setBranch(node, branch)
253
254
  return node
255
}
256
257
// helper functions for nodes
258
const LBRANCH = 0
259
const RBRANCH = 1
260
const EXTENSION = 2
261
const VALUE = 3
262
263
function setBranch (node, branch) {
264
  node['/'][LBRANCH] = branch[0]
265
  node['/'][RBRANCH] = branch[1]
266
}
267
268
function getBranch (node) {
269
  return node['/'].slice(LBRANCH, 2)
270
}
271
272
function getValue (node) {
273
  return node['/'][VALUE]
274
}
275
276
function deleteValue (node) {
277
  node['/'].pop()
278
}
279
280
function getExtension (node) {
281
  if (node['/'][EXTENSION]) {
282
    const len = node['/'][EXTENSION][0]
283
    return RadixTree.toTypedArray(node['/'][EXTENSION][1]).subarray(0, len)
284
  } else {
285
    return []
286
  }
287
}
288
289
function setExtension (node, ex) {
290
  if (ex && ex.length) {
291
    node['/'][EXTENSION] = [ex.length, Buffer.from(ex.buffer)]
292
  } else {
293
    if (getValue(node) === undefined && node['/'][EXTENSION] !== undefined) {
294
      node['/'].pop()
295
    } else if (node['/'][EXTENSION] !== undefined) {
296
      node['/'][EXTENSION] = undefined
297
    }
298
  }
299
}
300
301
function setValue (node, val) {
302
  if (val !== undefined) {
303
    node['/'][VALUE] = val
304
  }
305
}
306