├── .gitignore
├── Cargo.lock
├── Cargo.toml
├── readme.md
├── src
    ├── lib.rs
    └── main.rs
└── tests
    ├── simple.json
    ├── simple.min.json
    ├── types.json
    ├── types.min.json
    └── weird.json


/.gitignore:
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1 | /target
2 | /tests/vsat.json


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/Cargo.lock:
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1 | # This file is automatically @generated by Cargo.
2 | # It is not intended for manual editing.
3 | [[package]]
4 | name = "pick-json"
5 | version = "0.1.0"
6 | 


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/Cargo.toml:
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1 | [package]
2 | name = "pick-json"
3 | version = "0.1.0"
4 | authors = ["Gerard Rodes <gerard.rodes@omniaccess.com>"]
5 | edition = "2018"
6 | 


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/readme.md:
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 1 | # pick json
 2 | Read a single attribute of a json and stop there
 3 | 
 4 | ## how does it work?
 5 | instead of reading the whole json it stops reading bytes once found the picked attribute and its value is returned
 6 | 
 7 | ## run it
 8 | ```shell
 9 | $ cargo build --release
10 | $ target/release/pick-json tests/types.json emoji
11 | "🔥"
12 | ```
13 | 


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/src/lib.rs:
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  1 | use std::fs::File;
  2 | use std::io::{Error, ErrorKind, BufRead, BufReader};
  3 | 
  4 | pub fn pick_json (filepath: &str, property: &str) -> Result<String, Error> {
  5 |   let f = File::open(filepath)?;
  6 |   let mut f = BufReader::new(f);
  7 | 
  8 |   let mut is_prop = true;
  9 |   let mut found = false;
 10 |   let mut escaped = false;
 11 |   let mut is_reading_text = false;
 12 | 
 13 |   let mut buffer = vec![];
 14 |   let mut data: Vec<u8> = vec![];
 15 |   while f.read_until(b',', &mut buffer)? > 0 {
 16 |     // println!("BUFFER: {:?}", buffer.iter().map(|b| *b as char).collect::<Vec<char>>());
 17 | 
 18 |     let mut i = 0;
 19 |     'outer: while i < buffer.len() {
 20 |       let non_data_byte = buffer[i];
 21 | 
 22 |       if !is_reading_text {
 23 |         if non_data_byte == b':' {
 24 |           is_prop = false;
 25 |           i += 1;
 26 |           continue;
 27 |         } else if non_data_byte == b',' {
 28 |           is_prop = true;
 29 |           i += 1;
 30 |           continue;
 31 |         } else if
 32 |           non_data_byte == b'\n' ||
 33 |           non_data_byte == b'{' ||
 34 |           non_data_byte == b'}' ||
 35 |           non_data_byte == b'[' ||
 36 |           non_data_byte == b']' ||
 37 |           non_data_byte == b' ' ||
 38 |           non_data_byte == b'\t' ||
 39 |           non_data_byte == b'\r' {
 40 |           i += 1;
 41 |           continue;
 42 |         }
 43 |       }
 44 | 
 45 |       while i < buffer.len() {
 46 |         let byte = buffer[i];
 47 | 
 48 |         // println!("char[{}](rt: {} | prop: {} | found: {}): {:?} => {:?}", i, is_reading_text, is_prop, found, byte as char, data.iter().map(|b| *b as char).collect::<Vec<char>>());
 49 | 
 50 |         if escaped {
 51 |           // println!("\tscapped");
 52 |           data.push(byte);
 53 |           escaped = false;
 54 |           i += 1;
 55 |           continue
 56 |         }
 57 | 
 58 |         match byte {
 59 |           b'\\' => escaped = true,
 60 |           b':' | b',' | b'\n' | b'}' | b']' | b' ' | b'\t' | b'\r' if !is_reading_text => {
 61 |             let data_value = String::from_utf8_lossy(&data);
 62 | 
 63 |             if found {
 64 |               // println!("FOUND PICKED VALUE: {}", data_value);
 65 |               return Ok(data_value.to_string());
 66 |             }
 67 | 
 68 |             data.clear();
 69 |             is_prop = true;
 70 |             i += 1;
 71 |             continue 'outer
 72 |           },
 73 |           b'"' if is_reading_text => {
 74 |             if is_prop {
 75 |               // remove quotation
 76 |               data.remove(0);
 77 |             } else {
 78 |               data.push(byte);
 79 |             }
 80 | 
 81 |             let data_value = String::from_utf8_lossy(&data);
 82 | 
 83 |             if found {
 84 |               // println!("FOUND PICKED VALUE: {}", data_value);
 85 |               return Ok(data_value.to_string());
 86 |             }
 87 | 
 88 |             found = found || (is_prop && (data_value == property));
 89 | 
 90 |             data.clear();
 91 |             i += 1;
 92 |             is_reading_text = false;
 93 |             continue 'outer
 94 |           },
 95 |           _ => {
 96 |             data.push(byte);
 97 |             is_reading_text = is_reading_text || byte == b'"';
 98 |           },
 99 |         }
100 | 
101 |         i += 1;
102 |       }
103 | 
104 |       i += 1;
105 |     }
106 | 
107 |     buffer.clear()
108 |   }
109 | 
110 | 
111 |   Err(Error::from(ErrorKind::NotFound))
112 | }
113 | 
114 | #[cfg(test)]
115 | mod tests {
116 |   use super::*;
117 | 
118 |   #[test]
119 |   fn simple() {
120 |     assert_eq!(pick_json("tests/simple.json", "text").unwrap(), String::from("\"hi\""));
121 |   }
122 | 
123 |   #[test]
124 |   fn simple_min() {
125 |     assert_eq!(pick_json("tests/simple.min.json", "text").unwrap(), String::from("\"hi\""));
126 |   }
127 | 
128 |   #[test]
129 |   fn types_text() {
130 |     assert_eq!(pick_json("tests/types.json", "text").unwrap(), String::from("\"hi\""));
131 |   }
132 | 
133 |   #[test]
134 |   fn types_number() {
135 |     assert_eq!(pick_json("tests/types.json", "number").unwrap(), String::from("1"));
136 |   }
137 | 
138 |   #[test]
139 |   fn types_boolean() {
140 |     assert_eq!(pick_json("tests/types.json", "boolean").unwrap(), String::from("true"));
141 |   }
142 | 
143 |   #[test]
144 |   fn types_emoji() {
145 |     assert_eq!(pick_json("tests/types.json", "emoji").unwrap(), String::from("\"🔥\""));
146 |   }
147 | 
148 |   #[test]
149 |   fn types_min() {
150 |     assert_eq!(pick_json("tests/types.min.json", "text").unwrap(), String::from("\"hi\""));
151 |     assert_eq!(pick_json("tests/types.min.json", "number").unwrap(), String::from("1"));
152 |     assert_eq!(pick_json("tests/types.min.json", "boolean").unwrap(), String::from("true"));
153 |     assert_eq!(pick_json("tests/types.min.json", "emoji").unwrap(), String::from("\"🔥\""));
154 |   }
155 | 
156 |   #[test]
157 |   fn weird_escaped_n() {
158 |     assert_eq!(pick_json("tests/weird.json", "escaped_n").unwrap(), String::from("\"hi\\n\""));
159 |   }
160 | 
161 |   #[test]
162 |   fn weird_escaped_n_and_r() {
163 |     assert_eq!(pick_json("tests/weird.json", "escaped_n_and_r").unwrap(), String::from("\"hi\\n\\\\r\""));
164 |   }
165 | 
166 |   #[test]
167 |   fn weird_escaped_n_and_r_and_keys() {
168 |     assert_eq!(pick_json("tests/weird.json", "escaped_n_and_r_and_keys").unwrap(), String::from("\"hi\\n\\\\r,:\""));
169 |   }
170 | 
171 |   #[test]
172 |   fn weird_number() {
173 |     assert_eq!(pick_json("tests/weird.json", "number").unwrap(), String::from("1"));
174 |   }
175 | 
176 |   #[test]
177 |   fn weird_boolean() {
178 |     assert_eq!(pick_json("tests/weird.json", "boolean").unwrap(), String::from("true"));
179 |   }
180 | 
181 |   #[test]
182 |   fn weird_emoji() {
183 |     assert_eq!(pick_json("tests/weird.json", "emoji").unwrap(), String::from("\"🔥\""));
184 |   }
185 | }


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/src/main.rs:
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 1 | use std::io::Error;
 2 | use std::env;
 3 | mod lib;
 4 | 
 5 | fn main () -> Result<(), Error> {
 6 |   let args: Vec<String> = env::args().collect();
 7 | 
 8 |   println!("{}", lib::pick_json(&args[1], &args[2])?);
 9 | 
10 |   Ok(())
11 | }


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/tests/simple.json:
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1 | {
2 |   "text": "hi"
3 | }


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/tests/simple.min.json:
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1 | {"text": "hi"}


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/tests/types.json:
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1 | {
2 |   "text": "hi",
3 |   "number": 1,
4 |   "boolean": true,
5 |   "emoji": "🔥"
6 | }


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/tests/types.min.json:
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1 | {"text": "hi","number": 1,"boolean": true,"emoji": "🔥"}


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/tests/weird.json:
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 1 | {
 2 |   "escaped_n": "hi\\n",
 3 |   "escaped_n_and_r": "hi\\n\\\\r",
 4 |   "escaped_n_and_r_and_keys": "hi\\n\\\\r,:",
 5 | 
 6 | 
 7 | 
 8 |   "number":
 9 | 
10 | 
11 | 
12 |   1         ,
13 | 
14 | 
15 | 
16 |   "boolean": true
17 | 
18 | 
19 | 
20 | 
21 | 
22 | 
23 | 
24 |   ,
25 | 
26 |   "emoji":                                            "🔥"
27 | }


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