podlite/src/com/miniabs/Json.java

package com.miniabs;

import java.io.IOException;
import java.io.Reader;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

/**
 * Small streaming JSON parser that builds org.json objects straight from the
 * socket. Very long strings (episode show notes) are cut short and bulky keys
 * are dropped while reading, so a podcast with hundreds of episodes still fits
 * in the Galaxy Mini's small heap.
 */
final class Json {
    /** Keys never kept, at any depth. */
    private static final String[] ALWAYS_SKIP = {"chapters", "libraryFiles", "metaTags", "rssFeed"};

    private final Reader in;
    private final char[] buf = new char[8192];
    private int pos, len;
    private final int maxString;
    private final String[] deepSkip;
    private int depth;

    private Json(Reader in, int maxString, String[] deepSkip) {
        this.in = in;
        this.maxString = maxString;
        this.deepSkip = deepSkip;
    }

    static Object parse(Reader r) throws IOException {
        return parse(r, 2000, null);
    }

    /**
     * @param maxString longest string kept (longer ones end with an ellipsis)
     * @param deepSkip  keys dropped inside objects nested three or more levels deep
     */
    static Object parse(Reader r, int maxString, String[] deepSkip) throws IOException {
        Json j = new Json(r, maxString, deepSkip);
        int c = j.skipWs();
        if (c == -1) return null;
        return j.value(c);
    }

    private int read() throws IOException {
        if (pos >= len) {
            len = in.read(buf, 0, buf.length);
            pos = 0;
            if (len <= 0) {
                len = 0;
                return -1;
            }
        }
        return buf[pos++];
    }

    private void unread() {
        pos--;
    }

    private int skipWs() throws IOException {
        int c;
        do {
            c = read();
        } while (c == ' ' || c == '\n' || c == '\r' || c == '\t');
        return c;
    }

    private Object value(int c) throws IOException {
        switch (c) {
            case '{':
                return object();
            case '[':
                return array();
            case '"':
                return string(maxString);
            case 't':
                expect("rue");
                return Boolean.TRUE;
            case 'f':
                expect("alse");
                return Boolean.FALSE;
            case 'n':
                expect("ull");
                return JSONObject.NULL;
            default:
                if (c == '-' || (c >= '0' && c <= '9')) return number(c);
                throw new IOException("Resposta inesperada do servidor");
        }
    }

    private void expect(String rest) throws IOException {
        for (int i = 0; i < rest.length(); i++) {
            if (read() != rest.charAt(i)) throw new IOException("Resposta inesperada do servidor");
        }
    }

    private Object number(int first) throws IOException {
        StringBuilder sb = new StringBuilder(16);
        sb.append((char) first);
        boolean dbl = false;
        int c;
        while (true) {
            c = read();
            if ((c >= '0' && c <= '9') || c == '-' || c == '+') {
                sb.append((char) c);
            } else if (c == '.' || c == 'e' || c == 'E') {
                dbl = true;
                sb.append((char) c);
            } else {
                break;
            }
        }
        if (c != -1) unread();
        String s = sb.toString();
        try {
            if (!dbl) {
                long l = Long.parseLong(s);
                if (l >= Integer.MIN_VALUE && l <= Integer.MAX_VALUE) return Integer.valueOf((int) l);
                return Long.valueOf(l);
            }
            return Double.valueOf(s);
        } catch (NumberFormatException e) {
            try {
                return Double.valueOf(s);
            } catch (NumberFormatException e2) {
                return Integer.valueOf(0);
            }
        }
    }

    private boolean skipKey(String key) {
        for (String k : ALWAYS_SKIP) if (k.equals(key)) return true;
        if (deepSkip != null && depth >= 3) {
            for (String k : deepSkip) if (k.equals(key)) return true;
        }
        return false;
    }

    private JSONObject object() throws IOException {
        depth++;
        JSONObject o = new JSONObject();
        int c = skipWs();
        if (c == '}') {
            depth--;
            return o;
        }
        while (true) {
            if (c != '"') throw new IOException("Resposta inesperada do servidor");
            String key = string(512);
            c = skipWs();
            if (c != ':') throw new IOException("Resposta inesperada do servidor");
            c = skipWs();
            if (skipKey(key)) {
                skipValue(c);
            } else {
                Object v = value(c);
                try {
                    o.put(key, v);
                } catch (JSONException ignored) {
                    // NaN or similar; drop it
                }
            }
            c = skipWs();
            if (c == ',') {
                c = skipWs();
                continue;
            }
            if (c == '}') {
                depth--;
                return o;
            }
            throw new IOException("Resposta inesperada do servidor");
        }
    }

    private JSONArray array() throws IOException {
        JSONArray a = new JSONArray();
        int c = skipWs();
        if (c == ']') return a;
        while (true) {
            a.put(value(c));
            c = skipWs();
            if (c == ',') {
                c = skipWs();
                continue;
            }
            if (c == ']') return a;
            throw new IOException("Resposta inesperada do servidor");
        }
    }

    private void skipValue(int c) throws IOException {
        if (c == '"') {
            string(0);
            return;
        }
        if (c == '{' || c == '[') {
            int d = 1;
            while (d > 0) {
                int ch = read();
                if (ch == -1) throw new IOException("A resposta chegou incompleta");
                if (ch == '"') string(0);
                else if (ch == '{' || ch == '[') d++;
                else if (ch == '}' || ch == ']') d--;
            }
            return;
        }
        value(c);
    }

    private String string(int max) throws IOException {
        StringBuilder sb = new StringBuilder(max > 0 ? Math.min(max, 32) : 0);
        boolean cut = false;
        while (true) {
            int c = read();
            if (c == -1) throw new IOException("A resposta chegou incompleta");
            if (c == '"') break;
            if (c == '\\') {
                c = read();
                switch (c) {
                    case 'n': c = '\n'; break;
                    case 't': c = '\t'; break;
                    case 'r': c = '\r'; break;
                    case 'b': c = '\b'; break;
                    case 'f': c = '\f'; break;
                    case 'u': {
                        int v = 0;
                        for (int i = 0; i < 4; i++) {
                            int d = Character.digit(read(), 16);
                            if (d < 0) throw new IOException("Resposta inesperada do servidor");
                            v = v * 16 + d;
                        }
                        c = v;
                        break;
                    }
                    case -1:
                        throw new IOException("A resposta chegou incompleta");
                    default:
                        break; // \" \\ \/
                }
            }
            if (sb.length() < max) sb.append((char) c);
            else cut = true;
        }
        if (cut && max > 0) sb.append('…');
        return sb.toString();
    }
}